I'm sorry to hear that you're having a problem with gaming. Unfortunately, there aren't any settings that I can offer that would change or manipulate the game lag. If the audio is having a hard time working correctly, even using an inexpensive audio setup and routing the audio from the game console directly to, say a bookshelf system, would be relatively inexpensive compared to purchasing a whole receiver setup.
The game lag is there to help cut down on the lag, but maybe that would help with the audio part.
I'm using HDMI with my PS3 on this TV, and with game mode off, The settings are all adjustible and it sounds fine, but the game itself is nearly unplayable, for instance, I over aim in Call of Duty and I do much worse. With game mode on, the game plays just fine, But the sound is terrible through my tv speakers. A lot of the time, voices are hard to hear and muffled behind other sound effects, Turning it up or messing with any ingame settings wont work because even then, the sound effects are louder than the voices. It does this because game mode forces you to use "movie" sound mode, which sucks, and you can't turn it off. Is there any way to make the response time better with game mode off? I refuse to buy a $500 surround sound system just because samsung is likely in partnership with sound companies to force us to buy this crap.