The Sonos Amp has an HDMI ARC input, so that would work fine for your first use case, assuming your TV has an ARC output. Or, you could use an optical out on the TV to drive the Sonos optical to ARC adapter. 
 

In your second situation, if that CONNECT:AMP is unable to be upgraded to S2, replacing it with a Sonos Amp would allow you to wirelessly bond it to whichever Sonos Soundbar you have for that setup, also running s2. However, if that CONNECT:AMP can be upgraded to s2, you could use it without replacing it, by wiring it per the instructions in the setting up Amp or CONNECT:AMP as surround speakers FAQ.

With the first setup, get a Sonos Amp to power the in-ceiling speakers. Then connect the TV to the Amp using the HDMI ARC connection. Then connect the Apple TV to any of the TV’s other HDMI ports.

With the second setup, the Connect:Amp can be used as surrounds but your Sonos sound bar and Connect:Amp must be wired in one of the following configurations:

• Both the Sonos sound bar and Connect:Amp are wired to the router with an Ethernet cable.
• The Sonos sound bar is wired to the Connect:Amp with an Ethernet cable and another Sonos product is wired to the router.

If you want a completely wireless setup, replace the Connect:Amp with the newer Sonos Amp.

Thanks. Breaking them into 2:

• 1st set up: the TV is in the living room, w/o ARC connection. The Apple TV feeding it is in a media closet, with the current S1 Amp.  The TV doesn’t have an ARC connection as it is older. Newer Apple TVs don’t have other ports. I think I’m SOL on this set up, but not sure?
• on second set up, I know I need a newer amp as that TV has newer Sonos soundbar and speaker, so do I only just need the newer amp then ID the speakers as surround?