Not sure what you want to do exactly.
Is the combo amp like a Fender where the internal speaker(s) just plug into the back of the amp chassis ?
Are either of these amps tube amps ?
Franken amps are notorious for poorly done grounding. Do you get any hum when you just connect a wire between the chassis' ?
You might risk damage to one or both amps unless they are both OFF when you plug the cable between them. Can you do that or do you need to make this idiot proof ?
Is the combo amp like a Fender where the internal speaker(s) just plug into the back of the amp chassis ?
Are either of these amps tube amps ?
Franken amps are notorious for poorly done grounding. Do you get any hum when you just connect a wire between the chassis' ?
You might risk damage to one or both amps unless they are both OFF when you plug the cable between them. Can you do that or do you need to make this idiot proof ?