Nope, I think what Gonk is saying is that if you want to have a sub in the second zone, it depends on how you route the audio from the main room where the 990 is to the second zone/room.

If you connect the 2nd zone of the 990 to an amp located next to the 990, and then run speaker lines to the second zone/room, the thing to do is run the speaker fede through the "speaker inputs" on the sub, then to your speakers.

If you run line level audio to the remote room and the amop is there, then run the line level feed through the sub first, and then to the amp, and onward to the speakers.

Does that make sense?