Reviving this thread to add my experience with the M6.
For weeks I was having difficulty findning my tone and from ear fatigue from a certain frequency (even at very low volume) that I could not isolate and attenuate. The manual indicates that Bass and Treble knobs are parametric (middle knob is passive), so I was primarily concerned with finding the sweet spot for those frequencies since I figured the frequencies bothering my ears would be related. It never occurred to me that the issue with finding my tone on this amp was due to the Mids knob. I had never moved it beyond 10-2 during my initial experimentation because that's where I usually prefer it on other bass amps.
Of course, since Mids is passively wired, it never occurred to me to zero it out. I understood passive eq as "cutting", not as "boost only" so I would never think to leave it at 0. Until I did. And once I did, I realized that's where the tone I sought was located. By 0-ing out, I found the fundamental mids frequency I was looking for. Every other eq setting fell into place soon after. And as it turns out, it was the Mids frequencies that were being aggressively boosted (and hurting my ears) by my having at noon, what I thought was a "flat" setting. It is not; there is significant boosting at noon setting.
Anyway, I hope this may help someone still struggling with their M6. Start with Mids at 0, take it from there.
Cheers,
