Are you using the Dolby Digital AC-3 digital audio output? If so, it's possible that you are "doubling up" the bass by using both the ".1" bass enhancement channel of the AC-3 system and your regular speakers.
I'm not familiar with all the possible settings of your particular setup (I don't even know what other components you have), but this is a place to look if you have "extra" bass.
DennyD1@aol.com