How anyone can enjoy DT880s with leather pads is beyond me because I hate that cave-effect you're talking about. The leather pads sounded even worse on the 03 DT880.
Try the closedback mod if you want more thump in your music. The best thing about the mod is that it is highly tunable. You can make it as cold as a K701 or as warm and boomy as a Darth Beyer. ;-)