I agree, this app is remarkable for what it does, not perfect but useable.
Works well with Cubasis instruments but cannot get it to work with Sampletank.
I’ve tried all sorts of things, bought midi bridge etc.
Searching the net reveals IK has many probs with this, if anyone here knows how to get it to work let me know.
Hopefully Steinberg will come out with some high quality IAP instruments some time and make Sampletank redundant. 
Rob