Is kinda annoying.
My device has 2 zones, Master and Zone 2. Onkyo devices can have up to four zones. You can ask the device if the zones are powered, and it can say 01 for powered, 00 if off and N/A if the zone does not exist. So probing what zones are available should be just a matter of asking the power information, and ignore zones that say N/A, right ?
Nope, my 2 zone device answers for Zone 3 with a 00 and for Zone 4 N/A. Sigh...
Oh and no, I can't turn on Zone 3, it just answers with 00. And just for fun I plugged in a USB Sound card as I noticed the firmware contains snd-usb-audio.ko module, but no, no such luck, no Zone 3. Oh, yes, your Onyko runs Linux in case you didn't know that yet.