Congrats on the room. Secondly, I am not sure how good the Yamaha set-up utility is...so maybe an SPL meter from Radio Shack might be an option?

Lastly, I figure you may refer to this thread: BassTraps ala Sirquack which might provide you with some info. on your ordeal.

Also, you might want to have someone take a small mirror, and walk around the room (while you sit in the primary listening position) and mark off places where you are able to see the speakers. Then, you can create more 'traps' or hide the reflection zones. Others may be able to explain more, on this topic, however.

Good luck.