Is a custom audio system my only choice if i opt for the wagons?

Worry not! The wagon does come with a stereo.

For some reason, the 3D system is only an option on the sedan right now. Quite a shame becasue it is very good.

The places speakers go for the 3D system in the sedan aren't available for speaker placement in the wagon.

Interesting.....my understanding is that all of the same locations are in the wagon. Which locations aren't available?

No rear decklid.

Presumably they could just market a 3D 21-speaker system, or put two speakers in the cargo hold...but they don't.

Before I got my wagon I was bummed about the lack of the 3D audio system too, but my worries ended up being unfounded because the "standard" Burmester system in the wagon is really excellent (and I'm a picky audiophile). Maybe not quite as impressive as the 3D system, but that's more about special effects anyway––the wagon's SQ is very good and definitely not worth hacking up at some car audio shop. Don't forget it's still a huge upgrade over the base audio systems in the non-AMG E-Class...

I have been very satisfied with the std system in my E63s wagon.

+1 - not sure I would notice anything else

i love the sound in my wagon.... but i don't know what i am missing. (sure even if i heard it, i still wouldn't know)

I got the Banana when I had my 2018 E63 AMG wagon, it had horrible sounding speakers, not sure exactly how that happened but it sounded just awful. When I got my 2019 E450 Wagon new 14 months ago the sound quality was much better than the AMG even though it is the same command system. It had to have been something to do with the speakings in the amg wagon. I heard for a while Mercedes ran out of speakers and used some other vender with much cheaper lower quality speakers. My 2018 had to have been one of those cars.

I drive around in Sport+ and have the stereo pretty quiet. I can listen to music anytime, but that engine sing only when I'm driving.

Yeah, I have a wagon also and was always into the best system available in my cars, but I also find myself turning it down all the time... to hear the roar. Regardless of drive mode it sounds so good.