I've had good results with an Epiphan DVI2USB capture device. (Expect to have to do some fine tweaking of the timing settings to get a good quality picture.)
In my experience with OSSC it's not very useful for capture purposes. It can't convert framerate, and I think most HDMI capture devices you can find will have a problem with 70hz input from VGA 320x200. Only one of my monitors could handle its HDMI output for this case, and it wasn't useful to me because that monitor already had a VGA input I could use. Sounds like a few people use OSSC + a Datapath capture device?
I've heard of other capture devices from Magewell or Datapath that can handle low resolution VGA. (Maybe Startech too?) I don't have direct experience with them. I've also heard of upscaling framerate converters like the iScan Duo that might give easily capturable HDMI output, but they seem very expensive and are also going to be compromising the video by doing that conversion. (In general, capture devices that can handle this stuff seem a little more pricey than common modern HDMI capture devices.)