A excellent alternative to the S213 (W213) Burmester audio (810 type) is an amplifier with a digital signal processor (DSP).

[nicebubby8]

In an effort to assist other estate owners, both current and prospective, I'm writing this account of my experience upgrading the Burmester audio system as I was unable to locate much material that was particular to the S213/W213 estate when searching. Although you could find a lot of similar guidance on German YouTube videos for other Mercedes models, this piece is specifically tailored to the S213/W213 estate. I had high hopes for the Burmester system after driving a Golf R and a Touareg equipped with Dynaudio. That wasn't the case. What I did is this: I intended to make my stream-of-consciousness a little more readable, so please pardon the AI formatting.

The Issue: Burmester Letdown
My expectation was that my S213/W213 estate's Burmester system (500+ watts, "Premium Plus") would be on par with the Dynaudio setup in the Golf R.

Truth: The processing makes it sound processed but terrible, the effects are novelty rather than substance, and tweaking the equalisation yielded varying degrees of dissatisfaction. Personally, I wouldn't use it to play music.
My Opinion: I thought it would be appropriate to begin with the amplifier as that is where I would normally begin. It may be sufficient; nevertheless, I am sceptical because my prior experiences with this approach have only led to disappointment. Having said that, I have heard that simply updating the speakers can be sufficient.
My Process: Speakers After the DSP Amp (No Sub in the Boot)
My Path to Upgrade: We upgraded the sound by swapping out the factory amp for a digital signal processor amp. It was sufficient for me to cease and be pleased. Using one Haynes manual spanner, the process took around two and a half hours and was rather simple. A few days later, I upgraded the speakers—front and rear doors as well as footwell woofers, which Mercedes refers to as subs—with the increased RMS power that was available. The speakers were a rather involved effort that took up most of my day. I used two haynes manual spanners to install them. They are plug-and-play and are best suited for someone who isn't afraid to take apart the car's interior. In the end, I had a system that performs far better than the OEM Dynaudio in the Golf R. The burmester couldn't compare.
DC-Supported Amp Installation (S213/W213 Villa):
The stock amplifier is located on the boot's left side, which is a little inconvenient but still easy to reach. On the right side, conveniently located, is the fusebox. Surprisingly, the estate has enough for the new amplifier under the fake floor, either at the front or back of the boot.
Method: I collaborated with Horst from Allwoods Audio (a great eBay discovery). His recommendation to begin with only the amplifier was spot on. Actually, he offered me a tonne of advise and made me feel more confident; I had tried Allwoods since someone else had suggested them, and they were spot on. He made the change a breeze by providing a plug-and-play loom. Put the seats in place, loosen a few bolts to raise the floor, and you're good to go. A plastic lever, many torx screws, and clips on the right side of the fusebox provide access to the main feed, which is where power is supplied. You may find several earth points. Starting at the seats/seatbelt area and working your way backwards, gradually pushing the trim out and towards the front of the car, will save a lot of time and tackle the hardest part—removing the trim for the amplifier. Repositioning it involves pushing it in from the back and working your way towards the seat. As far as I can remember, the only screw you need to remove to access the trim (apart from the seat switch, which you need to unplug), but other than that, it's a simple matter of pulling and pushing. The seatbelt mechanism has a screw that holds a cover that you can take out.
For tuning, Horst provided the DSP with a respectable baseline equalisation, speaker labels, and pre-set crossovers. After I adjusted it to my liking, it immediately sounded considerably better, with loudness and clarity on par with Dynaudio. The low-end bass was noticeably enhanced, but when compared to a real subwoofer, it couldn't effectively generate the deep frequencies, therefore I reduced the low frequencies to less than 30Hz. I like Horst's settings for additional crossover points that I tried.
The outcome: The digital signal processor amplifier changed the game by itself, providing high-quality sound that would be more than enough for most people.
Enhanced Sound System:
I opted to upgrade the speakers to make the most of the increased power after enjoying the DSP amp for a few days. This was superfluous, but it made the system even better.
Acoustic Speakers for the Door:
To remove the door panels, use the two screws and clips that fasten them. To keep everything in one piece, use trim removers. Just removing the fabric coverings from the Burmester speaker grilles could improve the sound quality.
Installation: a simple switch that can be finished in a few hours across all doors. Speakers obtained at a reasonable price from Horst.
Mercedes Subs Footwell Woofers:
Elimination: More laborious. Although the carpet is thick and foamy, it fits back just perfectly and is difficult to fold. Unplugging and moving parts are the main concerns, while the bonnet release mechanism adds some complexity. Three 10 mm bolts are used to remove the speakers. Switch out the old speaker mounting with the new ones.
Setup: Took the better part of a day, but not impossible. Most of the time was spent on footwell speakers.
As a result, the system sounds better than the Dynaudio in the Golf R thanks to the DSP amp and the new speakers, which include improved footwell woofers. It has great deep bass. Even with cabin gain, 2 x 8" woofers can't compare to a 12" in a dedicated cabinet, but they're still more than capable of throwing a good party and delivering lots of power. By all accounts, these small 8-inch "subs" are now deserving of the moniker "subwoofer"; they sound far better than I had anticipated.
Just a heads up: the amp upgrading was a quick two-hour process, but installing speakers took the better part of a day. It would probably take a professional a lot less time (because to their organised tools and experience) to do the whole thing; I'd estimate 6-8 hours assuming they're careful and adding bespoke touches here and there. It would be logical for most people to stop at the amp.
Finalised: DSP Amp + Sub in the bootFor the average individual, I believe that the built-in subwoofer and basic speakers with digital signal processing would be sufficient. The footwell woofers will play louder music if you remove the low frequencies that are difficult to pinpoint. Not terrible, really, for door speakers. Aside from the fact that it's less work, all you really need is bass, and in an estate, this seems like a no-brainer.
Setup:
The frequency range of the footwell woofers is 65 to 150 Hz.
Headphones for the house: 150 Hz and up
Under 65 Hz, boot subwoofer
I intend to purchase and set up a subwoofer so that, even with the additional speakers, the footwell woofers I now have won't have to deal with extremely low frequencies. Alternately, you may do it in reverse. Although the new speakers have an improved sound, anybody familiar with digital signal processing can attest to its versatility. After turning off the center speaker, the picture improved dramatically, and time alignment resolved several issues.
Advice for Installing a Rear Amp in an S213/W213 Estate
I was unable to locate any estate-specific instructions, so I will describe what did work:
Place the seat down first and work your way to the seat belt cover.
Pull the trim toward you as you work backward. The clips are robust and easily removable with only a few screws.
Take the seat switch apart by disentangling its connector.
Instead of removing the floor trim from the tailboard, you should drag the loose trim toward the front of the vehicle.
The boot's side compartment is the perfect spot for a little amplifier. The estate's vast fake floor provides ample space for a larger one.
To access the power source, open the right-hand fusebox (using the plastic lever to release it), unscrew the torx screws and clips, and then fasten the fused live to the main feed. Feed the wire through while leaving the excess trim in place. Pick one of many nearby ground locations for a very short route close to the amplifier.
Summary: The Burmester Stock System is terrible and unsuitable for the S213/W213 estate's musical tastes.
My Workflow (DSP Amp First, Then All Speakers, No Separate Boot Sub): The DSP amp was a huge improvement that would have been sufficient; I then added speakers for much better quality. Easy enough for audio enthusiasts who aren't afraid of interior design to do, this plug-and-play project surpasses the Golf R's Dynaudio. Experts could knock it out in a day.
Most People Should Use This System (DSP Amp + Boot Sub): The simplest approach to getting high-quality, full-range sound from the standard speakers; it works great with the estate's boot speakers and the woofers in the footwell.
Best for greatest sound quality, especially in saloons/coupes, but more effort: Ultimate Upgrade (Amp + Speakers + Boot Sub).
A shout-out to Horst from Allwoods Audio. Dude is top-notch. He appears to be more interested in finding ways to save money than in spending it, and he's a total audio nerd. In addition, I would have insisted on having him handle the fitting if I were in the area, as I am confident in his ability to make adjustments that would expand the available choices.
Somebody in the future might find this useful, I hope!

[nicebubby8]

I attached the amplifier using a little piece of MDF. Underneath, you'll find the venting, which consists of two fans. The polystyrene insert object has a form that I customised, so removing the MDF will require some lifting.

[nicebubby8]

Easily removable fusebox (on the right)—no snap-out trim required. Comes with a removable sound chamber.

[nicebubby8]

After sliding it out with the help of the little plastic lever on top, you'll need to remove a couple of small levers and unscrew two torx bolts in order to access the area behind the live.

[nicebubby8]

To the left, you can make trace the yellow wire's path beneath the trim; I had to press on it a little bit to get it to emerge where I needed it. Easy as pie.

Everything is finished now; the only identifying feature is how well it sounds.

[mrnobady]

Appreciate the letter
Coming from an M6 with the B&O system, I was likewise let down by the Burmester system, therefore I'm taking a same path as you.


May I kindly request further information on the process of removing the boot trim in order to reach the current Burmester amplifier? I would much appreciate your assistance since I was able to remove the floor very simply but then ran into a wall.

Thank you

[mrnobady]

For the record, I figured I'd add some further information.

For whole panel removal, I discovered the plastic surround around the load cover mounting point on the left side of the boot to be the key. The only thing keeping it in place is a single pin clip, so you can easily take it out.