First Things First….
- Do not factory reset any Sonos speakers
- Unpair the Ones’ and Sub 3 from the Playbar before disconnecting it
- The One’s should revert back to individual rooms and not a stereo pair. If the latter occurs (although it should not) remove them as a stereo pair.
- The Sub 3 after removal should appear as “Unassigned”
- Now remove the Playbar and set it aside
- Reboot your router and let it come back
- Power Cycle your device
- Using the App Install the Beam 2 using the supplied HDMI cable using the HDMI eArc port if available. If not connect the Beam 2 to an HDMI Arc port. Test the Beam 2 for audio.
- In the room with the Beam 2 select add surrounds
- In the room with the Beam 2 Select add a Sub (you should see your sub as Unassigned)
- In the App set your surrounds to Full Stereo for music if you desire. They will auto switch back to surround mode after the music has stopped.
- Test your Sonos
To your second question….
IMO, The Era 100’s are a better speaker than the One’s. However, only you can decide if they sound better than your One’s. Personally, I don’t think Sonos would have designed them to replace the One’s if there were no noticeable difference/improvement in sound.
I have a Beam 2, with Era 100’s and Sub Mini setup in a guest bedroom. To my ear the sound is better as surrounds for movies and music. I also have Era 100’s as a stereo pair with Sub Mini in my garage,
Note: As with your Ones’ the Era 100’s cannot be used independent of a soundbar when used as surrounds.