I have to agree with Ken, it is time for some serious power. I have yet to run my 3808 for any length of time, a song or two, above -10 and this is really loud(~95-100db depending on the cd, IIRC) in my room. Your room size and what you are trying to achieve I feel are beyond the Denon's capabilities.
OK OK My classified ad will read as follows:
Denon 4308CI - surround sound amp, recently factory inspected and approved, still under warranty! Never abused, only used for playing Christmas Carols at our annual church get together.