I agree with what both Arnettpartners and BRF say.
Try reversing the monos back the way the were and let us know the results.
Swap Mono amps Left for Right
I had to disassemble my system and momentarily forgot which amp was previously left and which was right. I put them in swapped and I was much happier with the presentation. I think it may have something to do with my odd shaped room and maybe a different output level for the two amps? Not sure but I'm happy. Anyone try a swap just to see what would happen?