​​​​​​​Which Sonos speaker should I use as an auxiliary (not surround) speaker with an Arc Ultra?

Depending on the location and environment, Five or Era 300 if “humidity resistant” will be adequate, or Move 2 for IP56 water resistance. Note though that grouping a speaker and playing tv audio, there will be a small audio delay and lip sync issues which some folk find too great for comfort. The audio from Arc and grouped speakers cannot play tv audio in sync. 

Best is tough.

Best sound as a remote for the TV would be a Five.

If you also wanted music and Atmos is an option the Era-300.

Good but inexpensive an Era-100.

Considering the patio location though a portable, Roam or Move would be good. You could bring it in when not in use and wouldn't  need to connect power when it is outside.

Do you have more speakers that can only be used with the S2 app? If your system can be upgraded, that would be the simplest solution. Alternatively I would simply get a new Amp to pair with the Ultra, since you already have  speakers out on the patio.

I vote for the FIVE.

Note that there will be lip sync issues with any speaker that is Grouped with ARC. In this application the latency (75ms) will probably not be terribly disorienting. It is fortunate that there is some isolation from the ARC. Even if you didn’t install a dedicated speaker and simply ran ARC louder, there would be mild lip sync latency because the speed of sound is pokey at about one foot per millisecond.

I do have quite a few Sonos Amps and Connects that can’t run on the S2 controller (again, “thanks Sonos!”).

The Amp powering my current patio speakers is a newer model that supports S2,  I downgraded it to S1 since several of my other outdoor/backyard units aren’t S2-compatible.  Between playing music for the backyard or being able to be synced with the TV, I will choose the backyard music.

For now, I think I’ll go ahead with the Arc Ultra and a Five for the patio.

Hopefully some day Sonos can address any lip sync issues.

I’ve been reluctant to split my system across my property (about 2 acres, with a separate shop), but I’m leaning toward converting all the house units to S2 and keeping the older S1 gear for the shop, where I also spend a lot of time.

Any Sonos Amp should be able to run S2, as some of the CONNECT:AMPs. Only the first gen of the CONNECT:AMP would be S1 only. 

I see your vote and that is what I will go with.

That patio/TV area is really just an area for my wife and myself to sit around and BS with some Tennis or football on in the background.

Thank you everyone for the help, it is much appreciated!!