I think I should mention that 're-routing' the power supply involved scrapping the local +5V regulator on the MIDI board and taking the 5V from the OB-Xa power supply. That way I didn't get any voltage drop in the connecting cable due to the local reservoir capacitor being charged every cycle of the mains frequency. Since the MIDI board only draws 25mA and the power supply in the synth itself is more like 1A I figure the 5V supply can handle it. 25mA is just little more than a single LED so there's bound to be some margin there.

On the subject of CEMs, doesn't Doug at www.synthparts.com have a selection

/Ricard