[Wayne A. Pflughaupt]

Can one just place the microphone of the Galaxy SP meter up against the headphone diaphragm set to C-weighting and feed the headphone with REW's pink noise?

As Snatcher noted, measuring headphones is tricky. The reason is that they must couple with your head to get what you perceive as full-range response. Without the bass reinforcement you get with head-coupling, C-weighting won’t get you anything more than A-weighting will.

To get some idea of what C-weighted response would be, with a pink noise signal, I’d try setting the meter to A-weighting, and putting it against the diaphram. Then, turn on your main speakers, and set them at the same SPL reading you registered. Once you get the speakers at that level, switch the meter to C-weighting. No guarantees as to the accuracy of this recommendation, but it’s probably better than nothing.

Regards,
Wayne