Using a direct connection is just a way of narrowing down the source of the problem, and it's a lot easier than swapping cards. Too many variables with your current setup--especially if you've already tried everything on the software-side.
Also, swapping between an old AMD card and a new Nvidia card introduces too many other variables on top of that IMO. If it works, it doesn't help you any. If it doesn't, it still doesn't help you any. The Nvidia card and drivers have their own compatibility quirks (with the other components in your PC as well as whatever else the signal is passing through--like your receiver and your display). Could be hardware related, could be driver related, could be a handshake issue (originating from the card, the receiver, or the display). If I were you, I'd try to keep it simple until you get a handle on where the problem's coming from. But that's just my opinion. Others may have different suggestions.
If you've already uninstalled and reinstalled all the relevant drivers, games, and so on, I'd move into narrowing down a hardware culprit. Cutting out the receiver seems like the easiest place to start. From there, I'd move to trying different HDMI connections/cablees, then I'd try a direct mobo connection (bypassing the GPU). Hopefully, by then you'd know at least where the problem is coming from (though not necessarily if it's hardware or software related).
But just based on the error message you're getting, it still sounds software related. Switching between AMD and Nvidia cards can shake loose a whole bunch of potential software issues--especially if your computer had been using one for a long time. That's years of updates and customizations built around one card. Which is why uninstalling and reinstalling drivers and programs is the place to start.
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