Supported capture card?

We have 8 old cameras (non-ip type), and currently, we are using the included DVR box, and connecting to a network switch along with the BlueCherry host machine, and just tapping into the 8x RTSP streams from the DVR. Naturally, while this works, it’s not optimal.

It seems that Bluecherry supports Coax analog capture cards, but does it support any linux-compatible card, or just certain ones?

Any ideas as to where I would find a compatible card?