Room acoustics are probably the biggest problem for the OP. I'm surprised no one has mentioned this. The speakers and the room they are placed in dictate 90% of what you hear. If you don't like the sound change the room acoustics and speaker placement. If this does not solve the problem change the speakers. It really is this simple.
The amp is the last thing I would think of to improve sound quality. Unless what is being used is clearly not adequate then a new receiver amp may be considered. But not in this case.
