This is the HP50 thread, so I'll try to keep on topic (I think I can). Actually, I generally EQ out the recessed mid dip at 434Hz of the M-100 as well as the dip at 6300Hz (boosts at both frequencies). When you do that, the M-100 becomes very neutral-sounding. When I first did it, I listened to a classical music album and was quite satisfied. But my tastes tend to lean towards jazz as my username suggests. I still EQ there, too.
I'm thinking I don't need the HP50 if I have some EQ handy for my M-100. I still may try to give them a listen though. Maybe an Apple Store near me has the HP50 and the P7 so I can audition.