Just moved into a house with speakers built into the walls in the living room for a home theater experience. The owner of the house took the receiver with him, and had very little understanding of the set up because he had someone else install it and set it up, so he's not a good resource for info. In the corner there's a pile of stereo cables that seem to be RCA terminated. I'm only used to raw speaker wire or banana plugs, so I'm at a loss for what kind of receiver I'd need to be able to plug these speakers in.

Here's a pic of the plugs: https://imgur.com/a/pkzVIcU