On Monday, 2 March 2015 15:09:04 UTC+10, Mike the Strike wrote:
The only solution I can come up with is to use transformer coupling with three windings - two input windings from the two sources and one output winding to the speaker. The windings could all be on one toroid. The only coupling would be magnetic. I haven't had the energy to calculate what values might work, but offer it as a conceptual solution.

Mike

Interesting thought Mike, just wondering if the current in the windings of one output would not induce current in the other windings so you still would wind up with current backfeeding to the other amps.

I'll just go the conventional way for now .

Cheers

Paul