I think the crossbank manifold ruins the sound as well, the s63 doesn't really sound like a V8 at all.
The crossbank manifold obviously improves spool - but it makes it sound more like an angry 4 cylinder (it reminds me of the CLA45 and A45 actually) than any other engine, people often compare it to a V10, V12 and I thought it would sound like a flatplane V8 actually but it definitely sounds like an A45 to me. I don't see that there is a way to fix it, you can make it louder but it will still be the same weird sound.
https://f10.m5post.com/forums/showthread.php?t=588858