Hmmm....interesting question. Are you asking how you can control sources dedicated to a specific zone, or common gear, or simply how to change volume in the specific zone your in 'at the time' with your RF remote..

The Xantech unit your using only works with code group 68, having multiple groups wouldn't help.

I bet using a Xantech RT8 (addressable IR router) is a solution....take an IR output of your RF remote controls base station, connect that IR signal into the routers IR input, then, take each IR output from the router and parallel that with your existing Xantech keypads for the various rooms (at this point, it would be pure IR with no need for the 12 volts, connect to signal and GND). On your remote, you would have to make some configuration of panels and buttons (in the case of most cool remotes) that correspond with the rooms you want to control. Selecting that room would then route the IR through the IR router to the appropriate input on your existing multi-zone preamp. Of course, you would need to add the group 'extention' code to a macro on the remote for proper IR routing within the RT8.

It would take some programming effort, but if your starting from scratch anyway, this may be the most flexible way to solve the problem. The only thing your changing is the remote, not your existing keypads or IR distribution system in anyway.

I would be very interested in the outcome of this project!