Remember with monochrome it's all about the tone, rather than the colour(s) but you can also control tone using chrominance (colour luminance). It may be better to export your images slightly flat and without any additional clarity or maybe even backing off the clarity a little, because that can make skin look 'grimy' on otherwise smooth areas.
In SEfex try reducing mid-tone structure a little to prevent skin looking over-cooked, and also use the selective adjustment control points to control skin tones separately from the background if necessary.
Pop up a before (colour, image as exported to sFx) and after sample sample of you want specific crit/advice.
