Hi @Bernd,
You’re correct. Unify allows loading Midi Effects, Instruments and Aux Effects. I’m loading it as a Midi Effect (brown color) which then drives Spitfire’s BBCSO instrument.
Shane’s post in the Unify forum provided a solution to load the VST version of Scaler2 in the Midi Effects slot. It works now, and matches your screenshot of the Felt Piano, but doesn’t transmit the Felt Piano sound. Just the midi out now as intended feeding into BBCSO. So, it appears the issue may be AU specific.
Thanks!