uh ok, hear me out...
I would like to be able to use my power head as a stand alone power amp in this way.
I run my xlr main outs to a mixer in that mixer is my keyboard and "backing tracks" along with maybe a mic, then I run quarter inch outs from the mixer back to the return and alternative inputs on my Kemper as an aux which in turn is then using the built in power amp into a cabinet. Makes sense?
As of right now, if i do this I get an out of phase guitar sound because of the guitar signal only, everything else is fine.
In the meantime, would a simple phase inverter box of some kind work? Cheers!