And I am sitting now and listening MM-500 )))
Well, to my taste it is very much like HD-600/650 + extended bass + a little bit annoying high mids in rock/metal tracks.
If you are on RME UFX II with poort 3 band EQ, then you can use these settings to make it closer to the Harman curve.
Gain 5 Q 0.7 Freq 100Hz
Gain -3.5 Q 0.7 Freq 3000Hz
Gain 3 Q 0.7 Freq 4000Hz