Huh, that is indeed odd. Have you checked for updates for your Sonos? I’m wondering if there is a version mismatch between the firmware operating on your speakers (often automatically updated, depending on your settings), and your application version. 

I’d also be tempted to reboot my router, in an abundance of caution. 

Whichever route, I’d suggest that you stop ‘factory resetting’, unless told to by Sonos Support. As you’ve found, it rarely helps, and most often deletes any data that Sonos might read in a diagnostic to assist. In fact, I’d likely call Sonos Support directly to discuss it.

I’m using a powered pair of Shinola bookshelf speakers with the Connect. All firmwear is up to date (all of my Sonos gear automatically updates). Anything I stream from the app to the Connect sounds like a million bucks. I’ll give re-booting the route a shot, also going to try an actual Sonos RCA cable (as opposed to the cheap cables I had been using).

Appreciate the feedback!

My understanding is (never tested this myself) that there is a sensor inside those RCA jacks to determine if/when a cable is connected. It’s entirely possible your ‘cheap’ RCA cables aren’t quite long enough to hit that sensor….but there’s a whole lot of ‘guessing’ in that, I wouldn’t take it for gospel by any stretch. Better to do the testing, and possibly call in. 

8 different sets of RCA cables, no luck.

Then call in, I suspect. Must not have been that guess.