Macbeth,
I have a 990 and a 755 and I believe Gonk is right. When I first bought the equipment, direct from Outlaw, there was a trigger cable in the 755 box. I used the trigger cable (looks like a stereo cable to me) for a couple of days and as I recall the 755 light stayed on, but it was really in a standby mode. My 990 is now plugged into an always on jack in Bank 1 of the Panamax and it triggers the Panamax line conditioner to power on the 755 after everything else has been powered on. With the Panamax now in the picture, the 755 is truly off when I hit the 990 off button.
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Valdocs