You did not mention your budget...If you could afford it, the QS8s are a nice addition. The concensus around here on subs seems to be HSU or SVS. You will be amazed at how loud this system will play without losing sound quality, but if you want really loud playback you might consider the M60s...I have the M22s and can drive most sensible people from the room at about +5db on the HK-525
Whatever system you choose you will have the 30 return policy if you do not like your first choice.
You might try to find someone in your area to audition some axioms...There is a list of avaible sites in the Question and Comments thread. Whatever you choose enjoy.
