That's quite a setup!
Where is it all going to go? I guess you could do a third seat delete and stick it all under there, sans the subwoofer.
As I've become older, the only time I really turn up the volume is for my wife when a good song comes up from the 60's or 70's.

I'm no audiophile, but you are right in the lack of volume the ML has, but the fidelity, at lest for me and my wife, is really good.
From the looks of your setup, you agree, because I don't see any tweeters or midrange speakers, just lots of "boom-boom, thump-thump" equipment.
Should sound amazing when done!