I'd stay with the QS4 and VP100, since that Yamaha might have a bit of trouble with lower-ohm loads (The newer 1400/2400 are fine with 6-4 ohm loads but I've heard the opposite from Alan about other, older models).
Chances are, it'd be fine. 6-ohms isn't that bad. But you'd have a better fit (in theory, and, if you turn the volume up enough, in practice) with the QS4 and VP100 vs the QS8 and VP150.
Axiom's site has a room wizard to help figure out what speakers would be ideal for your size of room- it's a link off the front page, halfway down. It's one of those popup things so I don't know if I can post the link and it'll work.
Hope this helps!
