It does take up space, but it has solved a ton of my issues...

Over the summer I picked up an Extron 7SC. It accepts pretty much every analog input you can imagine. And it only outputs in RGBHV a.k.a... VGA. I haven't had an issue with any VGA sources I've plugged into it and the I got the thing for about $50 shipped with a remote for it. I did have to spend some more to get BNC to VGA cables..etc. But I've got the VGA out on it plugged into my OSSC and never had a signal the OSSC couldn't work with and send to the TV. I've also tested it just using my Sewel Hammerhead VGA-HDMI adapter and it worked well too.

Just an idea on something to try routing the KVM through to see if the signal from all the different systems doesn't sync better with the OSSC?

Hm, I don't think the problem is with the KVM really. AFAIK it's just an electronically-controlled analog mux. What comes in goes out, maybe with slightly less bandwidth, but we're not talking about 1920x1200 at 120Hz here, either. 😀

My problem is more that, with the 486, I need to move the picture over a little to the right to avoid cutting off the leftmost character in DOS. On the PII, I need to change the vertical active area in 640x480 so I can see the heads-up display in StarCraft. On the P4, the screen is WAY too far right and I have to bring it back left. etc etc..

The optimal fix would be to sit there for a few hours and find the ideal settings for every resolution from every PC, and save those to profiles. Then, link those profiles to load automatically when switching inputs on the KVM. But, that would take some engineering to find the input activation signal on the KVM PCB, and alert a microcontroller to send IR to the OSSC to load the corresponding profile. Doable, but hacky.

If I'm going to go to that trouble, I started wondering whether I might be better off buying a handful of FPGAs, ADCs, some memory chips, etc... and then just building an active VGA-to-HDMI converter for each PC based on an OSSC with minimal BOM.

I know such a thing exists (I think I even have one somewhere...) but I'm not sure if some $20 Amazon special would equal the output quality of the OSSC. Or maybe it would. That's why I'm thinking out loud. I know I'm not the only one solving these problems...

I understand what you are saying. What I was trying to say if that everything that goes into the Extron is processed through the Extron with a new VGA out signal. So I haven't noticed any issues with shifting video modes when I run them through the extron since it provides the same signal coming back out of it. I actually have the Extron providing a 720P at 60hz signal into the OSSC at all times. So again, it doesn't matter what signal is input into the Extron as it will always provide the same output signal I specify on in into the OSSC. Lag is quite minimal at about 4fps averaged.

Oh, I see. Sorry about that. I have seen a lot of people using Extron systems for console collections, but they were always just switch boxes -- or at most, would do some sync conversion.