I can't speak for Padres games, but I know it's fairly common on various RSN's for the audio signal to be 5.1, but for only two of the channels to actually have audio. I've even encountered a telecast a couple of weeks ago in which only the center speaker had audio, even though a 5.1 signal was being sent by the channel. It would be nice if the channels would only output the audio channels actually being used and allow us to use our AVR settings to control how we hear the sound, but apparently there are a number of channels out there that don't like to do that.
Better yet, do all games in 5.1 in the first place and be done with it.
Better yet, do all games in 5.1 in the first place and be done with it.