SONOS assigns very confusing names to their products. Your “Connect” has been replaced with “Port”. By the way, Connect and “Connect:Amp” manufactured after January 2015 are compatible with S2. The first four characters in the device serial number give the date of manufacture. “Amp” is the current replacement product for Connect:Amp. The word “Amp” is often used to refer to a generic 3rd party “Power Amplifier”. It’s confusing.
 

Here is the compatibility list. At the bottom of this page is instruction for accessing your SONOS account. Usually there is an indication here about S1/S2 compatibility of your players.

I’m not sure which product you are referring to with “dock”. If you mean “BRIDGE” this is not S2 compatible. “Boost” is the replacement S2 compatible product. Also note that, if you are able to wire a player to your network, BRIDGE/Boost is usually redundant.

Thank you Buzz. I have logged into my account and it appears I am not compatible with S2. I will have to check but my system is very old. Worth upgrading beyond Apple Airplay compatibility?

“Best” sound is very personal and only you know what sounds “best” (to you), but all of my friends who have replaced Connect:Amp or its predecessors with AMP feel that the sound has improved.

By the way, if the goal is simply to have access to AirPlay 2, you only need to upgrade one product. Install the replacement unit as an S1 unit, then you can Group other Rooms to the new product. Here are some details.

Thanks again. The system is so old I was wondering how long it can actually last but maybe run it until it dies.

Legions of the original 2005 units are still functioning. And, of course, some have failed. It is extremely unusual for modern hi-tech stuff to remain viable for almost 20 years.

If you decide to just buy one speaker for now, remeber not all new speakers do S1 anymore: https://support.sonos.com/en-us/article/sonos-s2-compatibility

Especially note that the One SL is S2 only.