S2 compatibility with play5, and connect amp

You haven’t provided enough information to know. It depends on which PLAY:5 you have, and which CONNECT:AMP. It’s entirely possible that you can run them all on S2. I’d recommend reading the announcements thread:

My Sonos system screen says for:

connect amp: Sonos OS; S1

play5: Sonos OS; S1

Frankly, I’m absolutely BS that Sonos would even consider developing a subsequent OS that

doesn’t support their own legacy hardware….if they don’t offer me a replacement for my amp and play5, I’m seriously considering BOSE.

When issuing off-the-cuff threats, one should do their research.  Bose recently abandoned an entire lineup of smart speakers that were being sold right up to the day they replaced them with a new line of smart speakers that were 100% incompatible with the old.  On the other hand, Sonos split with units that were designed well over a decade ago and haven’t been sold in 6 years.  

I am sure that you and Bose are made for each other.  Good luck.

You maybe right, but I’m still pissed!

https://community.bose.com/t5/SoundTouch-Speakers/SoundTouch-Officially-discontinued/td-p/561258

Boom!  Discontinued and replaced by a whole new lineup incompatible with a speaker you could buy the right up to that day.  If you dislike Sonos, you are REALLY going to dislike Bose.  

Yayayaya—I get it, I’ve got to suck it up. I don’t have to be happy about it though...

You can use third-party apps that can control both S1 and S2 systems from a single app.

Ok, what is the name of that app?

Depends on your platform. For iOS, try SonoPhone/SonoPad. For Windows, try Phonos Universal (which is mine).

I can’t see this in the App Store...

Which app? Where are you located? What OS are you running?

The iOS app you say can control Sonos s1 and s2 speakers from a single interface...

You didn’t actually say which country you are located in, or what OS you are running, but SonoPad or SonoPhone should be available in most geo app stores I would imagine and supports pretty ancient versions of iOS.

Installed SonoPad—it can see both s1 and s2 speakers, but only plays the s1 devices, even after drag and drop syncing...this is a recent iPad Pro, with the latest iOS.

Trying to sync the s2 speakers to the s1 speakers they come up empty...

SonoPad lets you easily control multiple systems on a single network, but its not a miracle worker: it can’t do things that are technical impossible, like connecting between S1 and S2 systems.