adding beam 2 to 100 pair + sub mini for music

Not much ‘setup’ required. If it were me, I’d probably remove any surrounds and subs that are connected to it in the controller, change the Beam to another room name, and then group it during playback with the existing Eras and Sub mini, although I suppose if you wanted, you could integrate them as a new 5.1 room. If it was just music playback, I probably wouldn’t. Then I’d connect the existing surrounds and Subs to the Arc Ultra. 

Firstly, you want to remove any surrounds/Sub from Beam 2 in order to replace it with the Arc Ultra.

Rename existing Beam 2 room to something else (room names can be easily changed in the app, so not an issue even giving it a temporary name).

As the Beam 2 is capable of Atmos, if you subscribe to a music service that provides Atmos then you’ll likely want to create another surround system in the other room. To do that, you would need to remove the Sub Mini from the Era 100s and then separate the stereo pair. You will then be able to add the Sub Mini and Era 100 as surrounds to the Beam 2.

You may also consider placing the Beam 2 in another location (kitchen?!) depending on how satisfied you are already with the Era 100s in the other room or whether locating the Beam 2 in the other room enhances the existing sound.

I have a Beam that as yours did ended up in a non-TV Room. Small bathroom and no spare room so I didn't hook up surrounds or a sub, still sounds quite good streaming or Grouped to my Arc Ultra so I don't miss any TV action on potty breaks. The spouse really likes it as it is almost invisible sitting on a cabinet, much less obvious than the previous Play 1s.