How to control matchbox audio outputs

Is there a way to control the matchbox audio output assignments?

I’m using headphones and I would prefer for Left to use output 1 and Right to use output 2. But it is using output three, thus I can’t hear it unless I change stuff in my RME mixer, (I’d prefer not to do that).
Any suggetions?

Strange that it’s using output 3. It should probably be defaulting to 1 and 2.
If you can send a matchbox log file we can see if there’s anything unusual in te audio engine setup for your machine.