Have you seen this:
http://www.cypripedium.de/forum/Defl...0seedlings.pdf
They seem to recommend inorganic media for seedlings (perlite + pumice). I believe that Cyps from Spangle Creek Labs are still juvenile. For the adults of this species, one person recommended 1 gallon of rich garden soil (or MetroMix 560 SunCoir) + 4 cup of limestone (or oyster shell) grit.
I'm also getting some Cyps from Spangle Creek Labs, so I'm not an expert. My previous attemp failed, so I'm gathering info, too.