With one controller.  Is there a way I can do this?  I have a PS4 and a PS4 Pro-... and, it just hit me, that my set-up isn't able to take on recording from 2 consoles at once.  Well, let's solve one thing at a time.  I need to be able to use a single controller on both the PS4 and the pro at the same time.  Will a USB splitter of some kind, work?

FYI: The AM4 platform only allows capture cards to work in the X16 slot of the motherboard.. which is where I would like my GTX 1080Ti to be, so, despite having two capture cards, I can only use one.  That is the absolute only problem I've had since switching over to Ryzen, though.

I have no help to offer, but can I please ask why you want to do this thing? Are you planning on doing comparison videos?

i.... really dont know. what your describing here is kind of confusing, im still not sure why you would need to do that or what it would accomplish. but there are USB splitters that can do that (theoretically)

just search for a 'female to male' USB splitter and you should find what youre looking for

Use 2 controllers. Bob's your uncle. That will be more functional than any single controller solution, if that's even possible to begin with.

Even if it would work, in many games the gameplay would differ after a few seconds anyway because the NPCs behave slightly different or one console starts the level a second earlier or dynamic weather...

That's fine.  I would like for them to be as close as possible.  I would like to even potentially throw PC versions in the mix too, at some point.

I could have sworn I hit "Sony"

Obviously

I'm pretty sure Dualshock 4 uses Bluetooth for controls even when it's connected via a USB cable. I think this might have been changed in a more recent controller revision, but I'm not sure at all about that.

Have you tried 2 sessions of remote play at the same time?

When I connect the DualShock4 to my PC and then start the Remote Play app, the contoller input works even if the app ain't the active window. It even still works when you change the Windows user account!

If you then start the Remote Play app in the second user account again, it could be possible to connect to the second PS4 with the same controller without disconnecting the first PS4. Since I don't have two PS4s I only was able to test it until the second Remote Play settings started.