Axiom Home Page Forums General Discussion Home Theater Crossover Settings

Hi there,
I recently (like today) finished setting up my HT. For audio, I have the Onkyo 600 connected to M22Ti (front), QS4 (surround), VP150 (center) and EP175 (sub).
There is a crossover dial on the back of the EP175, and the Onkyo 600 has crossover setting at 80 / 100 / 120. I am assuming that the receiver setting and the sub dial settings must match, right? Is it better to select the highest crossover the reciever supports?
Also, another unrelated question is since the onkyo supports 6.1, which rear center speaker should I get? can I buy one QS4 instead of a pair?

thanks,

- Asim