Is it on all games, or just a few?
It sounds like it's probably just a case where the game developer was simply lazy, or blew the majority of the game dev budget on the graphics, leaving little for anything else. So, what I'd suggest is you try some game that has the audio mixed rather well. Final Fantasy XIII and Uncharted come to mind. Maybe rent them, borrow them off a friend, or just buy them since they're both great games.
Also, I know on games like Uncharted, there are multiple selectable audio tracks. Since I have a full fledged home theater setup, I make sure to select the DTS 5.1 audio track, but if I were just going to be using my TV speakers, I would want to drop that to stereo or I'd be missing out on everything that wasn't on the L and R channels. So, be sure to check the game options, make sure the audio isn't set to some kind of surround sound track.
But since we're experiencing the same problem with two different consoles and two different TV sets, that really only leaves the game as being the problem.
Have PS3 hooked up via Playstation HDMI cable to Samsung 46" LED HDTV. I actually have two PS3's, both of them hooked up in the same manner, only to different televisions. Both of them are expressing the EXACT same problem. It appears as though the center channel in way muffled and being cut out. The action scenes are significantly louder. i've tried EVERYTHING, at least I think. Configured audio settings both automatically and manually, messed around with dynamic range control, boosted the audio in the PS3's menu to +4. There are So many settings within the PS3, could I be missing something. Something just doesn't sound right, clearly. Both PS3's I have hooked up are exhibiting the same issue, and both are hooked up the same way, via HDMI directly to my televisions. I don't see how this could be a compatability problem, since both are having the same audio problems. Just can't figure out why the spoken dialogue/center channel seems muffled, as though it's being dropped. i know my TV's only have two speakers, so I only have 2 channel selected in the PS3's menu (configured both manually and automatically). I really need guidance here. It's been driving me mad for years!!!!!!!