[Thuneau]

I own a good measurement mic that I use for work. It's an Earthworks M30 . I also have access to a B&K 4006. I was looking into getting a IEC711 coupler to measure and EQ my in-ears. But unless it's a B&K or Gras it will most likely come with a cheap element and without a calibration file.
I see a lot of IEC 711 couplers on ebay around the $80.00-$200 price point. Can those be used with external microphone through an adapter? The descriptions in the ebay posts are very vague and sparse.
I would appreciate any help picking the right parts.