One of the things I'm struggling with is where to plug the cables into the Yamaha coming from the 990's zone 2. I've poured over the Y's manual and I don't see anything that would be the likely plugs to use.

Can anyone give me an idea of what to look for?

The manual does illustrate input jacks coming from a tape deck or recorder. Is this where I would plug the zone 2 cables in to?