I would have thought that the Mic input would have been overloaded via the headphone output, normally Mic inputs are very sensitive, there also may be an impedance mismatch. It's a while since I owned a 6000, or even a 7000 for that matter!!, but from memory if you use an expression pedal you can set it to ignore the Mic, so that no matter what level you are playing, the Mic. is constant. Walter.