Yes it's a good deal.
You can place them pretty much anywhere, but if you've got a 7.1 system, and the QS8's are your only multi-directional surrounds, I would indeed place them at the sides and use your direct firing speakers in the rear.
Having said that, it may be fun to try them in both places and see which you prefer.
Lastly, I wouldn't ask Axiom about the swap. It's just not cool. If you'd bought product from them in the past, perhaps I can see asking for a favor, but that's not the case here.
Good luck and enjoy those new QS8's! They're killer surround speakers.
