Hi. As far as I can tell, your subwoofer outputs are only for the main zone. You have at least a couple of options to add a sub, and here are two:
(*) The one with the best bass management and likely the best sounding would be to get a sub with speaker-level inputs and outputs (that are filtered using a crossover in the sub), run the Yamaha speaker-level outputs for Zone 2 to the sub, and then run the speaker-level outputs from the sub to your ceiling speakers. The kicker (as I'm sure you realized as you read that first sentence
) is that would probably be a real pain in the a** with the way you already have things wired up.
(*) Run the Zone 2 line-level outputs from the Yamaha to a sub and adjust the crossover dial on the sub to try and get it to blend in with ceiling speakers. Probably won't sound too bad, and people do that same thing, but the issue is that the sub and the speakers will be getting a full range signal. That's not a problem on a sub with a crossover dial because you can adjust the frequencies that the sub plays - but not the ones that the ceiling speakers play. So, there will be some overlap. Might not be too bad, though.
