I'm going to have to agree with This Guy's post. It's going to hard for you to find a better value for under $500 in HT. Onkyo, while I've never heard this particular gear, impressed me with it's Integra line.

I would preface my opinion with the fact that you have a relatively large room @ 15' X 25', and you'll probably be pushing the unit to distortion if you listen to HT at anything close to standard theater levels.

DTS theater specs call out 105 dB max volume (at seats) , and a surprising 115 dB from the .1 or sub channel! With BOTH of my subs, I can just about get there. This is of course a transient reading, for things such as a cannon shot, or explosion, and would never be for extended passages or we would all be deaf after leaving the theater! Most people never set volume at this level anyway, so your probably fine.

Oh, I also like that they rate the receiver power into 4 ohms in the specs. This tells me that your receiver will have no problem if you want to upgrade to speakers that might have a lower impedance. As it stands though, with you wanting it for mostly X-box, sports TV, and HT in that order, I think you'll be happy with what you have out of the box.