It sounds like we have almost IDENTICAL setups and I’ve probably tried all your possible combinations, so I hope I can help you here. 😉
First I’ll start by saying playing a game via your PC monitor through the capture device is a no go. It adds way too much lag, probably anything from 0.1 to 1 second of delay.
My original setup was a SCART matrix/splitter with one signal going to the CRT TV and the other going to a Sync Strike, which then plugs into a StarTech PEXHDCAP (basically the older version of your USB capture card) via a VGA cable with a VGA to DVI converter. I don’t know about the USB3HDCAP but my older PEXHDCAP it has an audio jack for audio in so it was easy to get sound and audio in from the Sync Strike. If your capture card doesn’t have an audio jack input you can still feed the audio into your PC’s line in and use OBS/XSplit to use that as an audio source. I did use a SUPER quality triple shielded 3m VGA cable for £4.99 ($7 US). The cable should have been more than 10 times that. Its actually a very beautiful cable if you appreciated things like that ;). With this VGA cable the quality of this setup was great and people made a lot of comments about the good quality, but it was lots of wires.
I’ve since removed the sync strike and use the OSSC, so I have a scart CRT feed and a HDMI OSSC feed (and now a HDMI Splitter).
All this boils down to what equipment you already have and whether you want to keep the CRT and how much you are willing to spend.
Lets start by talking about getting the signal to your computer. I’m sure you know what the OSSC and Sync Strike can do but here are the basic advantages one over the other
The Sync Strike has two basic advantages
1) is more plug and play (to some extent, it doesn’t need any sync strike setup but may need more fiddling on OBS/X-Split)
2) is about 1/8th the cost of a OSSC.
The OSSC basic advantages are
1) it can clean up the analogue signal giving a sharper/better image.
2) it allows use of HDMI cables, which will carry audio meaning fewer wires, as well as more accessibility of cables. HDMI are cheap, easy to get hold of and will be more supported than VGA/DVI on future capture cards.
3) SCANLINES, obviously! Scanlines are hit and miss on streams and youtube, but I set it to the lowest setting 6%, which on a good quality stream gives a nice hint of a scanline, but on poorer quality stream compression kinda blurs them out.
4) more flexibility for other consoles, as it has VGA, component and scart inputs.
5) no need for a scart splitter, which are expensive and not easy to get hold of.
6) once the OSSC is setup for the Super Nintendo there’s less fiddling in OBS/X-Split (aspect ratio correction etc)
Next, what do you want to game on?
If you have to have CRT, you will need a scart splitter and then its down to whether you can afford a OSSC.
If you are willing to play on a digital screen (LCD/LED) you could use the OSSC and then a HDMI splitter to split the signal between a monitor and your capture card. The splitter I use (Which cost about £20) states it will not create any additional lag my simple tests does support that.
I have a cheap gaming monitor (about £100), decent screen, low lag, crap sound, and that is between 0-1 frames behind my CRT TV. I’ve then tested on an old LCD TV and that had about 3-5 frames of lag. I’ve played reaction games like Sonic the Hedgehog on the old LCD TV and I thought I was losing my abilities it as it felt I wasn’t reaction quick enough to parts of the game, I thought I was getting worse at the game. Playing on a gaming monitor it felt just like the CRT and I was reacting quickly.
But as stated it all depends on what equipment you’ve got and how much are you willing to spend.
I think I use the best setup for you which gives great flexibility but you need the equipment.
Console -> Scart Splitter ├-> CRT └-> OSSC -> HDMI Splitter ├-> Gaming monitor └-> Capture device
If you have a scart splitter but don’t have/cant afford OSSC
Console -> Scart Splitter ├-> CRT └-> Sync Strike -> Capture device
If you don’t scart splitter you need an OSSC
Console -> OSSC -> HDMI Splitter ├-> Gaming monitor └-> Capture device
Here are some youtube videos using my setup.
This one is a scanline test using the first setup. Its a PC Engine and I was testing the quality of the scan lines.
This one is an older video and using the middle setup (scart switch and Sync Strike).
Sorry if this was so long and ended up being useless. Please feel free to ask me any questions. If you want I can do a comparison between a Super Nintendo via Sync Strike and OSSC and upload it to youtube.