What;s the problem with the receiver that you think it needs upgrading? I'l still using a Denon from that time period and it still sounds great. Of course, I'm not using the same speakers you will be.
I'll tell ya right now... no receiver is gonna sound good through those speakers, at least for serious listening. Background, maybe, but not for focused listening.
FWIW, there's never much activity in the rear/surround speakers in most movies.