Got a response from EDCOR. They recommend:
WSM6400
1/2W stereo unbalanced line level signal to a mono unbalanced or balanced line level signal
$10.23 each.
http://edcorusa.com/p/220/wsm6400

Thanks. Do you think this Edcor model would do the trick? http://www.edcorusa.com/p/143/wsm600-600http://www.edcorusa.com/p/143/wsm600-600

WSM600/600
1/2W 600 Ohms to 600 Ohms (1:1) line level matching transformer.

I'd like to make a simple passive "Y" splitter to feed two amps even if the amplifiers have large "ground" voltage differences. The "BigShot ABY" appears to do that but I can't find the model of the transformer used in the circuit and I don't need the A-B selection abil...