Is it on all games

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.