If I open Dorico SE (v6.1.10.6078) alone, it plays the accompaniment fine.
If I open Pianoteq Stage (v9.1.0) alone, I can play my keyboard on it, and it works fine.
But I want them both working together! The problem is, the sound stops working in Dorico if Pianoteq is also opened (either first or second).
It’s a mystery for me how to get Dorico to play accompaniment while I play keyboard via Pianote at same time.
I’m on Windows1 10.
Pianoteq is using ASIO4ALL v2.
What if you try with the Steinberg Built-in ASIO Driver (in both, Dorico and Pianoteq)?
Also, try to start Pianoteq prior to Dorico in order that Dorico does not occupy all MIDI In ports.
I did not test with Pianoteq, but with the HALion Sonic stand alone app and Dorico, and that did work for me.
On the other hand, you could also have everything running just in Dorico. You go to Play mode and there highlight the Piano, then all MIDI input data shall go to the corresponding slot in HALion Sonic and you can play along with the playback from Dorico.