I don't know any manufacturer that allows digital inputs for zone 2/3 if they are just stereo outputs. Integra does offer a unit with full surround in zone 2, so I would imagine that digital is allowed for that unit's zone 2.
EVERY other manufacturer that I know of, requires analog. Denon, Sony, Yamaha, Onkyo (Integra), HK, etc., etc.
It's one extra set of audio cables to shoot audio to a second zone... It's cheap to hook up and will sound good if you just hook everything up correctly. You should be very happy with the setup using analog.