My usb digital piano does not appear in the input pulldown for instrument tracks.  If I play on it, I can see the data in the midi monitor. But none on the track (yes it's armed).
I can get it to work IF I create 2 external instruments as so:

number 1

• receive from : Steinberg UR242
• send to: Digital Piano

number 2

• receive from : Digital Piano
• send to: Steinberg UR242

MAC: S1 version 6.1.1