Hi

1. Yes, you can play to the Arc/Sub combo, I do this with my beam. 
2. Nope! The Arc/Sub are linked, just like you can’t select an individual device in a Stereo pair.
3. You can select the TV at the source for the TV room. I am not sure if it will auto switch over of you’ve grouped it and I can’t test it right now. But I know you can select the TV as the source if you have override it. Y

You can also play whatever your listening to on TV across your other Sonos speakers, great for sports gatherings if that's your thing... just music off the cable box etc. 

Its fairly flexible! Other than the sub/arc - I wish I could have the sub as part of two rooms. 

Thanks @britishwonderings.  For item #2, what if I just buy the Sub.  Can I group it with all of my other Sonos speakers when listening to music?  If so, why wouldn’t I be able to do that if I added an Arc to the network?

Hi,

Maybe I misunderstood. 

The sub needs to be paired with a speaker set/room. If you pair it with the Arc then it’s wedded to the Arc and will only play when the Arc is in use. You can’t then say, play music in the kitchen and add the sub, you would get the Arc and Sub playing. I hope that make sense. 

You can un pair with the Sub and move it, but it’s a pain to do every time. 

You can but it as a set or individually, that makes no difference, whatever is cheaper. 

@britishwonderings Hmmm….. so the Sub MUST be paired with either a stereo pair or a soundbar?  Could it, for example, be “paired” with 5 other speakers?  I’m beginning to think it’s solely designed for TV listening and not to enhance general music listening when the TV is not involved.  Thanks again for all of your input.

Pairing (2 speakers paired together as stereo) or bonding (Sub or surrounds bonded to other speakers) are different from grouping.  Pairing/bonding are semi-permanent and done via a fairly involved process from the Settings menu, whereas grouping is not permanent, and done on the fly via a grouping button.  Also, the Sub cannot be standalone.  It must be bonded to another room.

Can it be grouped as its own device?  Or is it bonded to another speaker (speaker A) and therefore part of the group when speaker A is added to the group?

If you want both tv sound with the Sub and hifi/music with the Sub, you can bond the Sub with the Amp for both. It will switch between music and tv sound. For tv it will deliver you a virtual center speaker. Bonding the Amp with 2 surrounds for tv is even beter. Connect 2 high quality passive speakers to the Amp for music and you are done. Works great for me!