Thanks for tidying up after me, Altec.

Here's a simple test: use the RCA cables you were using with the ZD to connect the 990 to the A5 and give it a listen. Unless you get something nasty (hum or buzz), there's no harm in migrating to that permanently with the 990 and you can much more easily incorporate a little audio switch that allows both the 990 and ZD to share the left/right channels of the A5.