I had big success when I moved the VP100 from under the TV to on top of the TV (using one of the omnimount shelf things). It very noticably cleaned up the dialog for me.

I doubt the VP100 is choking on that 80-100Hz content. Are you sure you're not just driving the Marantz into clipping?

I don't think it could hurt to try the Denon. It'll take forever to wire everything, though.

bibere usque ad hilaritatem