If you put any video card to the RignEdge, or a flashed, card, etc, it will boot and you will get video, etc, up to the Segaboot (The screen that shows you the RingEdge logo), then you will get an error message and only low resolution video output.
What happens then is the same that if you put a new video card in to your PC and you don't install drivers, you will get a 640x480 video screen or if you are lucky a 1024x768.
When you install drivers in your PC, all the drivers references a concreted video card with a specific Windows GUID, VID and PID,etc, if you change the video card for one indentical from the same manufacturer, you will need to reinstall drivers again.
On the RingEdge is worst, because the file system on the SSD is mounted as read only , is windows embeded and has EWF (Enhanced Write Filter) installed, so that way the SSD is not corrupted when you power it off, without shutting down the windows properly.
But in any case if you change video card, even if you are lucky to find one that can be flashed with sega firmware and works, you will never been able to install a game from DVD and keychip.
During the installation from an original DVD+ Keychip, lot of signatures are compared and if something is not original, the Installer just shows you an error and refuses to install.
Your best chance is try to buy an original RingEdge video card in Yahoo auctions, they appear there from time to time, or get a new RingEdge in Yahoo auctions, sometimes are sold for just 1000 yens, even if the RingEdge is not working, you can get an spare video card.
Have you or anyone you know attempted this and failed trying to do it?