Anything better than 90 dBV (note dBV and not dBr) would be considered good on a power amp, and anything at or above -100 dBV excellent. On dBr measurements, a good figure (power output dependent of course) is better than -115 dBr, but on large well-engineered amps, -120 dBr.
With a distortion analyser, you have to make sure the measurement setup is not the cause of the problem wrt the mains harmonic spikes. Try disconnecting one channel completely from the load and shorting the input and then run the measurement on just the other channel, what do you get?
With a distortion analyser, you have to make sure the measurement setup is not the cause of the problem wrt the mains harmonic spikes. Try disconnecting one channel completely from the load and shorting the input and then run the measurement on just the other channel, what do you get?