How do you connect the RGB output of a PVM to an XRGB-Mini?

[Monitor]

Hi, searched through the forum but couldn't find a definite answer on this. I have a PVM-20M2U monitor with a SCART-BNC adapter to connect most of my consoles via RGB. What I'd like to do is use the passthrough feature to connect the PVM's RGB output to the XRGB-Mini and be able to display the same console on either/both displays without switching out cables. I built a custom 4x RCA to 8-pin XRGB-Mini cable and got BNC-RCA plugs from Monoprice: http://www.monoprice.com/product?c_id=1 ... 1&format=2

Whenever the BNC plugs are connected to the PVM's output ports, the brightness on the screen gets turned up way too high. This happens whether the other end of the cable is connected to the XRGB-Mini or not. I know the PVM I have has auto-terminating ports, and the BNC-RCA plugs I got from monoprice are "rated to smoothly transfer 75ohm signals" but I don't have any other information on them. Is there a specific type of adapter I need to get this to work?

I've tested all the ground pins/connections on both sides of the cable so there's no issues there, but I'm guessing there is something wrong with my cable or BNC plugs that is causing this. I just wanted to know if anyone got this setup to work without affecting the PVM's screen brightness, and what parts/cables they used.