Thanks for the questions, here are the answers: The unused channel did have signal (input from the tuner - which I can't disconnect) and no output because the balance was all the way to the deck speaker channel and I only had the one deck speaker connected on the "B" speakers. "A" speakers are a matched pair inside, and I never ran A & B together, always either/or. I didn't have to turn the volume up any higher to hear well on the deck but this might be something - I also have audio output jacks on a TV in the same room, and I sometimes played the TV audio on the deck speaker. I do have to turn the volume up higher when listening TV than with the receiver tuner to get the same volume level, but that's just to the 12:00 position (or halfway) where I'm probably just at 9:00 on tuner. This older receiver has CD, LD, Phono, and Tape inputs and I ran the line out from the TV to the LD inputs.