The Two zone answer is a grabber -- you HAVE to have that analog signal (not on CD, but on DVD) when you want the signal available to the second zone.

I ran into and odd reason, that I have never researched beyond this example: We had a Toshiba surround DVD in the early days of DTS that had a track on it which would only output sound on the analog jacks! It is a recording of a Japanese orchestra, and I was really impressed with how quiet the background level was until they started playing, and it was just as quiet. Adding old-fashioned RCA cables fixed this, and that is now standard with all we do.