Hybrid solution to existing home

I have researched a centralized AV distribution solution for my home, but have decided to go with a hybrid of centralized audio for Party Mode audio and a de-centralized AV solution for each location.

Party mode is from a speaker wire hub in a structured panel that has 2 channel audio out to 6 locations. The hub has a single speaker wire input from my family room receiver zone B that plays to all 6 locations from the panel. Each destination has a volume control with amplifier in the wall plate for that location. All was pre-wired at home construction 15 years ago.

In each location, I plan to have a TV with an Amazon fire stick for streaming and either a soundbar or small HT speakers in or on-wall. The Fire Stick supports my Sony ps vue streaming service, so I can have 5 different connections concurrently including local networks. So each location can be tuned to different ps vue channel or Netflix, etc as needed.

Finally, I am experimenting with a Raspberry PI 4 B at each location to connect to the TV via HDMI and wirelessly to my network for browsing and NAS content.

The challenge I am facing is how to integrate the Rapsberry Pi with pre-wired speaker wire solution. I was thinking a wall plate with input selector would work, but couldn't find anything that would take speaker wire input from the hub as 1 input and either RCA or line level cable as 2nd input. Any suggestions?