The Bridge was succeeded by the Boost, that is S2 capable. You could also connect a Sonos device (not a Sub or surround) via cable to your router to have the system (except Era’s, Roam or Move) switch over to Sonosnet.

Well, the Sonos BOOST replaced the Sonos BRIDGE, it will run either S1 or S2, and has newer and faster hardware. It does appear (maybe?) to being deprecated at this point, though, so you can either wire any Sonos device to your router directly, or simply hang your Sonos system directly from your Wi-Fi signal. 
 

Edit: slower typing ;)

@whiskeyrobber Reading you post and the intended use, “to connect an existing home stereo (amp, speakers, etc.) to the Sonos system”, did you possibly mistake the Bridge for the Connect?

The Bridge (now succeed by the Boost) was used to get the Sonos devices on a separate wifi net, but the Connect could be used “to connect an existing home stereo (amp, speakers, etc.) to the Sonos system”. The Connect is succeeded by the Port, the biggest difference between the two being the Port only has a coaxial out, where the Connect had both a coaxial and an optical out.

The Connect Gen 2 (built from mid 2015 on) is also S2 capable by the way.

Sorry, I meant to reference the Connect. I have a Connect V1. When that goes, what options does Sonos provide to connect to my home stereo amp? 

Port as a Connect replacement.

Several other options if you just need a Line-In connection. 100, 300, Five have a Line-In option.

Maybe Move and Roam but I have neither.

eBay often has used Connect Gen 2 devices which are the cheapest option.