I needed to install Winamp to hear Shoutcast stations as the internal player does not yet support URLs.
I have temporarily disabled the internal player so I only have zone 1. The master volume control has no effect on Winamp, so the music controls overlay slider has no effect. The music player volume works fine.
I did substitute the master up/down (+/-) buttons on the overlay with music player ones just to get some control. But, how do I assosciate the master with Winamp?
(I feel another DOH! coming on)