Hope that doesn't look too dumb as a post title but I was wondering where the sound I hear through my Onkyo receiver and M22 speakers comes from when watching a TV show, and what effects the quality?

I've noticed some television shows sound wonderful and others not so great so I was wondering if I'm not using the TV speakers then the source of the sound is what? The station itself? And does HBO (or any station for that matter) send a clearer signal and that gets processed through the tv tuner then through the receiver?

Does the the TV tuner have an effect on sound quality? Like if I got a killer latest and greatest tv would the sound be better, or is it only the recevier/speaker combo and the processing in that receiver that effects the sound?

Am wondering because it seems some shows sound better but I'm not sure if that's true what can I do to make them d sound better.

Thanks

Larry