Hi - can't tell you what the problem might be with your system, but...
The THX standard for surround sound levels is: dialog 75dB and loudest sound 105dB. So if you're reading 100-105 dB at your viewing/listening position, your system may really be OK?
Using Terminator II Special Edition (re-mixed and remastered in THX), and using the recommended levels (at the viewing position), the loud passages will rock you out of your chair. Dolby and DTS levels are approximately the same as THX (I would have to go back to my references to find exact playback levels for each encoding system).
I have tested the 75/105 dB standard on all of my THX movies, and in fact, if you set the dialog at 75 dB - the loudest passage is right at the 104-105 dB level.