Era 100 & Beam 1

You should be able to ‘group’ the two rooms for music streaming without any difficulty, however when ‘grouping’ while using the TV input on the Beam, there will be a 75 ms delay between the Beam’s ‘room’, and any ‘grouped’ room. 

If you set tne Era-100s up as a a stereo Pair Room or as two additional Sonos Rooms you can then Group them with the Beam. Streaming will work perfectly, TV sound will have a slight delay.

If you aren't familiar with Grouping tap the small speaker icon with a number next to it.

Edit, I type too slow!

"Additional speakers" in a Beam setup aren't beneficial.  As stated, they will be delayed for TV sources, and they will be repeating all channels, with the Front Left-Center-Right, Surround Left-Right, and Atmos Left-Right all coming from the front, screwing up any surround/Atmos effects, and muddying up the front soundstage.

If the ERA 100 speakers are in another area of the house not within earshot of the Beam there may be some value grouping them with the Beam.  Sometimes when we are eating dinner we like to listen to the network news.  So we group a pair of Move speakers with the TV system in the living room.

I Group a speaker in the bathroom for TVso we don't miss any action during potty breaks.

I have speakers in the kitchen, and an open floor plan, I find I'm better off turning my Arc Ultra up a bit than Grouping the two Rooms for TV, the echo really irritates me.

Have you set them up as two separate systems? If, as they should be, they are in the same system, you should be able to see all three speakers (which, presumably, you’ve set up as two rooms).