The Connect Gen 1 will continue to be supported on the S1 app with bug fixes and security updates, but it will no longer see full updates with new features.

Ok.

Since there is another app for this, there is no way to connect rooms with different generations?

Is there only Port and Connect that is able to connect with an already existing hifi system?

If the Sonos speaker is only compatible with the S1 app, it cannot be grouped together with a speaker that is only compatible with the S2 app. But most Sonos speakers are compatible with both the S1 and S2 app. Here is a full list of compatible speakers:

https://support.sonos.com/s/article/4786?language=en_US

You can connect a Port, Connect, Amp, or Connect:Amp to an existing system.

Connect Amp or Sonos Amp only if you do not already have an amp in the existing system.