Bill, I have the Barry MS40s and, if memory serves, there is a protective circuit that prevents blowing the tweeters. Unfortunately, Barry is weak on publications and Service Manuals. The protective circuit I'm thinking of would "throttle back" rather than die, exactly as you've described. You might call Barry Tech Support. I understand that they've improved 1000% recently. My loyalty to Greg Mackie gave me pause before buying them. No problems so far.

Just noticed your input. You could have an impedance mis-match. IIRC, the MS40 RCA inputs are 20KOhm. Have you tried using TosLink? I'm using the Optical TosLink inputs. Maybe try a TosLink cable.