I do not believe this is possible - the volume control affects all the audio outputs at the same time - you cannot adjust one without the others.
The other option is to create a separate volume adjustment on your DSP / external Room Audio and not use default the Touch10 volume control. You could then put a macro on the RoomKit that sets the volume back to the default level every time it is changed just in case someone does try to adjust it with the Touch10. You could present this additional volume control on to the Touch10 using the In-Room Conttol functionality.
Wayne
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