This feature already exists. You can send audio to an unlimited number of buses if you are using Artist or Pro. If your audio interface has more than 2 outputs you can go into Song Setup and enable more physical outputs. In my example my interface only has 2 outputs, but this is the menu where you would configure additional outputs. Even with a 2 channel audio interface you can add an additional set of outputs that could bypass main so you can audition a reference track or mixdown track without mix bus processing.
If you have an 8 output interface (4 stereo pairs) you can add 3 buses in addition to main and assign each bus to a separate set of outputs.
You can see here that I added a bus and assigned to a different set of physical outputs than main. I set the bus pre-fader so the level is consistent: