I like listening to music the way it was intended. CD's are in 2 channel, so I listen to them in stereo. DVD's are in multi-channel, so I listen to them in that form. Mostly in DD as I don't have DVD-Audio capability and there aren't as many DTS tracks.

My DVD movies are always quieter than music in ANY of the formats. That goes for both DVDs and CDs. It's just the way they're made. I really don't have much on both CD and DVD for the same music, just Blue Man Group. The DVD is louder, but I haven't bothered to check if that's because there are more channels being used (more energy bouncing through the air) at the same time or because it's been recorded louder. My guess is that they're similar. I think you have to have the same tracks by the same recorder/composer, otherwise you're introducing extra variables that can not be accounted for.

Spend the time to get the setup right. If done really wrong I could easily believe a stereo playback would sound better. There's less interference and fewer things in the wrong places at the wrong settings.