I have purchased the M60s and the VP150 and I love them. I'm using my old mains as my current rear surrounds for the time being. They are the Polk Audio RT800 floorstanders. Should I buy the sub next or go with the QS8 surrounds first? Opinions welcome!

Axiom M60s, VP150, QS8s, EP500 -- Rotel 1075 & 1068 -- Panasonic BDT500 -- Panasonic 60S60