I was thinking of a similar cause along that line -- the glitch may be in the Y cables that somehow reroute the signal flow. The Y connection takes place before the amp input jacks, and that makes them possible culprits. But the two boards are on a parallel- not serial- hookup, with signals being sent out from their output jacks! At any rate, I appreciate your input, and may have to follow your advice and add a mixer into the line. Thanks, DonM.