It seems to me that the solution is right in front of you, no? Just figure out which of your two customers is less attached to their unit.
Or you could tell them they're both SOL, and if they abandon them, you could make one working unit to sell on Audiogon . . . nah, don't do that.
Or you could tell them they're both SOL, and if they abandon them, you could make one working unit to sell on Audiogon . . . nah, don't do that.