Allow Main Fader to be assigned to a DCA

Requesting to create feature parity with XM32. This would be a wonderful quality of life improvement for those using X Air series with an Aux fed sub for example, both Busses could be assigned to a DCA and their level controlled together.

In my usage scenario, I send to FoH from main outs and then use additional Aux mixes set as subgroups (But not sent to Main) as a rudimentary matrix output to send to Subs/Broadcast etc. Ideally one DCA would control all Bus masters together but currently Main fader cannot be assigned to a DCA