Do any of the Sony XA-39 owners know if there is a "master" input on it?

When I had a XA-39 it worked like this: My kenwood HU was "master" and Empeg was "secondary". So long as the HU was powered on, it played through the XA-39. When I powered the HU off, it would switch to the Empeg if Empeg was connected.

This was good behavior as it allowed me to power up the Empeg and turn the output way, way down before turning off HU and switching to the Empeg. Since I would have the output set to max for home use, I generally had to go through this maneuver or suffer bad speaker juju.

Anyone know where I can find a XA-39 now?

Sorry, no. I haven't yet seen one come up on eBay, but I expect one will someday.