I have made good experiences with my s/h rocks. And I have come to really distrust sphag-anything, since it tends to promote rot. So I really think you are going the right root here. I have my onc in only s/h rocks and I mist the new growths every morning, which they seem to like. All that misting would never be viable with sphag or bark mix since it would grow all sorts of things.

And go get a root-boosting fertilizer. Mine is made by COMPO and has done good work, no idea if it's available in the states. But I was looking for superthrive when I found it, so maybe try that.