If both the Arc and the Amp are wired to the same switch, distance shouldn’t be an issue (being aware of CAT-5s network distance, it isn’t infinite, but should be an issue in a home environment). 
 

Yes, in music mode, they would be ‘secondary’ to the Arc…however, if you change the room settings to have the surrounds be in ‘full’ mode, and boost their volume relative to the Arc in music mode, they’ll be effectively stereo. You’ll not be able to turn off the Arc, but it would be much quieter, and you’d be getting full stereo from those ‘surrounds’, rather than just support for the Arc. All in the surrounds settings for the room that contains the Arc, once you bond them. 

thats very helpful, thank you. I don’t have any sonos soundbars so have no experience for those settings.

To be clear, there are two different “modes” and in music mode I can have the volume levels of each speaker set differently than in movie mode?  if that is the case, this is a no brainer for me. just want to make sure i would not have to manually change that setting depending on what i was listening to.

Umm. Not sure I explained that properly. The Sonos system considers a soundbar, subs and surrounds as a single room. You can adjust the relative volume for two inputs, the TV input (HDMI-ARC, most frequently) and streaming input (generally music, but any source other than the TV’s digital input). This volume adjustment allows changes between the front device (the sound bar, which has Right, Center, and Left channels) and the surrounds (which have Right and Left channels). Normally, surrounds are set up in ‘Ambient’ mode, which means they’re supporting the sound coming from the sound bar. Sonos offers the option, when streaming to them, to change them from ‘support/Ambient’ mode to ‘Full’ stereo mode. You can’t (as I recall) change anything beyond the volume difference between the ‘front’ device and the ‘surrounds’, so you don’t have control over each speaker individually, but each ‘group’ of speakers, specifically front and surrounds. Balance is reserved for TruePlay, if needed, but I’ve got some rooms I’ve never bothered with it…I consider it to be mostly marketing hype, if you’ve set up your speaker locations properly. It can help, in some situations, but isn’t a ‘silver bullet’, in my opinion. 

thats even more helpful in clarifying things, so thanks alot. but that fucntionality is exactly what i need AND allows me to easily add a sub which i have been unable to do in the past because it would be too far from my Port. it’s not the cheapest solution, but i think the best.