At the risk of completely missing the point of what you’re trying to accomplish, the main benefit of the OSSC is taking retro consoles to modern TV’s without lag. Why not use it for that purpose, replace the PVM’s with inexpensive but decent flat screens, and open up the possibilities for displaying and capturing? This would also solve your “separate monitors” issue, as you would be using flat screens always.
To that end, you can introduce a DVDO product like VP20, VP30 or VP50, into the mix. You will have to chain the OSSC and DVDO, ahead of monitor and capture device, then split the output to monitor and capture device. Placing the OSSC first will minimize the lag and keep the deinterlacing away from the VP*, which some models don’t stay low-lag once deinterlacing is involved.
So for example, if you have a game that switches between 480i and 240p res modes, set the OSSC to 480i line2x and 240p line3x. Set the DVDO to 720p or 1080p output (if your capture device supports 1080p adequately). The DVDO will maintain 720p/1080p output through the game’s display mode switches and your capture device shouldn’t have any issue with it (maybe a brief second of a blue screen during the switch, but it’s better than losing connectivity completely).
I’ve been toying with chaining both directions – OSSC -> VP30 and VP30 -> OSSC. No noticeable lag introduction in either scenario.
You probably need various powered switchers/splitters to achieve the final solution and depending on the consoles and how many at once you are feeding into the chain.
Hope this helps and I didn’t miss the mark completely.