No dongle, please! Only as an option.
I prefer to keep server away from internet too, but it is not a big problem to share connection from phone for 1 minute. All your expenses - 1 usb wi-fi dongle.

USD56 is the price for new chineese converters (which can do up to 3G SDI)
All your signals will be sd, so you can find really cheap old used converters sdi to composite.

2 Decklink Duo2 (495*2) or 1 Decklink QUAD 2 (995) + SDI Distribution Amplifiers Blackmagic Mini Converter SDI Distribution (6*195$, 8 outputs each)+some cheap sdi to composite converters from ebay (56$ each) .

It's a joke, not an advice.
Actually i switched back to R5 for a while because if this and another couple of glitches.

You can syphon it inside Resolume with Airserver app, or capture from AppleTV and Airplay

Same issue. I posted here. Hope it will be fixed next update.

You can try to disable HDMI audio and check again.

Not HP, custom built. If you use DXV content, all content is decoded on your videocard, there is no parallel work for your CPU, and no way to make good use of CPU multi threading. Running 40 layers is an extreme task, i think. No surprise that you can not get good fps. You can check GPU load with GP...

Mine runs at 2,5. So it is not frequency.
If you use DXV - videocard decodes files.

And also you need to read something about PC. What ports exist, which of them are inputs, which outputs, what signal they can take or send, how to distinguish regular usb type-c from type-c with DP Alt Mode and from Thunderbolt3.