I have a Connect:Amp being used to connect a turntable (Line In) to my living room. Currently it’s just a Beam but the plan is to add Ones or Symfonisks for 5 channel surround. My question is if I use the Sub Out from the C:A to connect to a third-party powered subwoofer, will it provide the missing .1 or would it just send out a generic low level signal? My assumption is the latter, since the Sonos app forces me to create a separate room for the Amp that I can only group with the Beam room. If this is the case, is it even worth it to go the third-party route or should I just save up for a Sonos Sub instead? Setup would be used equally for music and movies/TV.

When playing TV sources, the Amp (and thus the 3rd party sub) would lag behind the TV by about 70ms.  If the Connect:Amp is connected to passive speakers, they would also be playing the non-sub woofer channels and would also lag behind, not to mention repeating what the Beam/surrounds are playing. This would not make for a great listening experience. 

I see. So I guess the “sub out” option on the Amp is designed more for controlling a separate set of speakers altogether and not so much running in sync with a Sonos home theater setup?

I guess that means I should start saving my pennies for a Sonos SUB...

Yes, that is the case.  Although you can use the Amp and passive speakers as the front L/R of a home theater with a phantom center.  Which would allow you to use a 3rd party sub as the .1.  However, that would make the Beam redundant.

For clarification, @jgatie is referring to the current Sonos Amp above, not the older Connect:Amp.  The Connect:Amp can’t be connected to a TV for TV audio to run the front L/R speakers.