"It seems to have separate input for IR via its own wired in zone controllers (one for each zone). It's not very clear to me how you get the usbuirt to talk to these (6) different controllers. "
Wow, what a headache. You would have to buy 6 different USBUIRTs, then use Girder (via Xlobby) to individually activate the specific USBUIRT for the zone you want to control. Or for almost half the price, you can get a 6 zone 35 Watt per channel amp with automatic zone power-up (when music is sensed).
http://www.htd.com/12channelamp.html With the money saved you could get 2 PDA's for FULL control of your music.
Rant On: I've asked it once, I've asked it a million times. How the hell are you going to navigate through a MP3/album collection with a keypad if you can't see what you are browsing? And why the heck would I want a keypad on the wall except for the fact that it looks cool? Has it not already been established that we are lazy people and we want to control our AV remotely from our seats? That's the whole reason why we use remote controls in the first place! :Rant Off
I think you will find that keypad controls have poor utility in any reasonable sized music library. This is why a client/server system as is used in Xlobby is THE best solution. Although more expensive, several PDA clients (you could also use a cheaper Palm based PDA if it has a web browser, or if the room already has a PC, you can use that as the client) will prove to be a more practical solution.
Good luck.
hjackson