Congratulations Joe! I'm sure you're going to be very happy!
I have an Axiom 350 that I'm happy with in my 13' square room. I've never heard an SVS or an HSU. I know that many swear by them, but I'm no sure that will be the case in the future now that Axiom has some bigger subs that evidently compete with the best out there. It might sound trite, but a factor for me was the fact that my sub is in a very visible spot and I wanted the finish to match my other Axioms'... which are finished very nicely by the way! The system that you're considering: M60s, VP150, QS8s and 350 is my system exactly.
You may have read on this forum that the QS8s are very forgiving, and I've found that to be the case. Firing sound in four directions definitely eases "critical placement" needs! Mine are about 3' above, and 1 1/2' behind a seated listeners' head. My couch (listening/viewing position) is right up against the back wall, and the speakers in that position reflect a little off the back wall I think, spreading the sound out a bit more. I think they sound great there, but I think the diffuse nature of them will enable them to sound good anywhere nearby!
I'm sure others will have some specifics for their situations as well!
