Guess I'm too late....but For party speakers, the last thing you want is a surround sound system. I would Have gone with powered PA by JBL, Peavy etc. And daisy chain them. From there, invite your guest to bring their own mp3 players and set and forget. Advanced programs with DJ features in an IPad for example will give you all the flexibility you want. The stuff is bullet proof as they are made for professionals and the cheap mp3 players are more than sufficient in sound quality when partying. In the right size and placement, subs are unnecessary.
All sound from each speaker should be mono which is ideal for parties with everyone moving around. Dump the receiver idea. They are totally unnecessary for this use and prone to abuse. You will have total individual volume control over each speaker and all the flexibility you could hope for. Our group does this (we all have a couple of the PA speakers) in the business we are in and for parties, it works great.
Powered JBL Eons on stands and strategically placed would do the trick, but a
plethora of other choices that sound as good but heavier if you done't have to move them much. Other brands from Behringer for example, sound very good and are much cheaper for example.p The only other option I would consider is a cheap mixing board with an EQ.