Ok, let me try to understand:
MAIN in Halion is not like MAIN in an audio interface. I know MAIN as a Master Channel that takes all the individual audio signals and sends them to the final output (e.g. Loudspeakers, Headphones).
In case of Halion MAIN is just an output channel like all the others (thanks @Derrek ).
If I create two pianos in Dorico with Midi Channel1 and 2, send those two into Halion then Dorico expects to get the audio back from Halion on OUT1 (=Main) and OUT2 - ist that right?
Dorico then sends the audio from those two to its own MAIN Out (the slider on the right in Dorico’s mixer) - is that also right?
If - for example - I like to have Piano2 on OUT3 in Halion, I would need to assing Channel 3 in Dorico.
If I understand that correctly, there is no free routing of the signal possible in Dorico. If it outputs to Halion on Channel1 it wants the signal back on OUT1.
Did I understood this right?