Help with overly "bassy" dialogue, please

[dwesson]

I've had my 5.1 system set up the same way since January, which is when I upgraded to Blu, and I have been generally happy with it. My speakers are hand-me-downs from my father, and the receiver I'm using is an Insignia NS-R5101. Nothing special, but good enough for where I'm using it right now.

Recently, I've begun to notice that dialogue, especially male dialogue, sounds bass heavy... if that's how I have to describe it. It gets sort of muffled and annoying to listen to. I notice it most when watching LOST on Blu, and haven't really had a major problem with it outside of that.

My question is, what settings do I need to adjust in order to eliminate that sound? I'm pretty clueless when it comes to audio, so any help would be great. Here are my current receiver settings in case it helps:

Subwoofer: On
Tone: Off
OSD: On (I'm not really sure what this even is)
Front Speakers: Small
Center Speaker: Small
Surround Speakers: Small
Subwoofer: Yes
Crossover: 80Hz

Then for my channel levels:
FL: 0dB
C: -4dB
FR: 0dB
SR: -2dB
SL: -2dB
SW: -2dB
DD: 0dB
DTS: 0dB

And finally, my PS3 audio settings:
Connection Type: Optical
Audio Output Format for Optical: Bitstream

Thank you to anyone who responds!