Emu XL-7 & MP-7 User's Group

I'm setting up a new XL-7 (well, it's used of course, but I just bought it) and having trouble 
with external MIDI control. I used a another XL-7 for years in my studio, and never had this 
problem.

Audio connections are good, and the XL-7 transmits MIDI just fine to external devices. The 
MIDI activity LEDs show that it's receiving MIDI input - but that MIDI input won't trigger 
sound. I've tried swapping MIDI cables, changing ports on my MIDI interface, setting my 
external keyboards to different MIDI channels, and have gone over every Command Station 
parameter I can think of. 

I'm stuck. Any ideas as to what the problem is? Have I missed something?

This XL-7 has OS 1.0 installed, and I'm wondering if that has anything to do with it. My 
previous unit was 2.0.

Cheers