One more comment about the M6 treble control. I just checked the manual, and it states that when cut, the treble control reduces frequencies from around 750hz to around 3.5K. So, that control almost acts like an attenuator for the mid driver in the fEARful cabs (an oversimplification, I know, but relatively accurate according to my ears and their published specs on that control).
So, that is a wonderful head for having a powerful, simple control over the top end of the tone of the fEARful. Really sounds 'sweet' at about 9 o'clock, which basically seems to take the 18sound down about 3db in the upper mids, and still lets a bit of top end definition while reducing the 'clank' that cab happen with some basses, etc.