Well, this is what I'd do in your situation, first I'd triple check to make sure that it isn't something as simple as a speaker connection. Seems you have already done this. Next I'd check the audio connections to and from the TV. If everything is fully seated and it still displays problems I'd replace the interconnects. I think it's rare that this is where the problem would be but we're running low on DIY repair options. If the problem persists I'd switch to only the TV speakers and try to find if sound was coming from both speakers on the TV. If not then somehow perhaps the problem is in the source? I'm reaching here.

Without resolution I'd keep a decent sized stack of DVD's nearby and fake it.

good luck,
jc