It’s not that complicated.
You connect your external streamer preferably via Ethernet connection to your router. If you got something with WiFi it will connect up to your WiFi Router, but wired is always better than wireless.
You run your player software on your PC and it serves your streaming services and audio files via the NETWORK to your streamer. None of that PC noise makes it from your PC into the network and to your network streamer.
Your PC monitor still shows Album Art and music playing progress just like normal. What you are doing is running a separate simpiler “computer” that does only one thing – deliver network audio to your DAC.
Why didn’t others tell you that’s what you need? I’d guess your local audio guy doesn’t sell streamers or isn’t into serious streaming. But if you’re moving up to a Halo Spring 3 KTE you are into serious streaming. And, the folks at Halo don’t want to complicate things they want you to buy the DAC, letting you figure out everything else.
Will USB out of your Windows PC work? Of course. Will it work well enough? Surely. Will it provide optimal sound quality? No, not really, but good enough if you’re not seriously into streaming. But then you wouldn’t be buying a Halo Audio Spring 3 KTE if you weren’t seriously into great sounding streaming audio.
PS. Someone else will have to help you with J-River. I’m a dedicated Roon user and wouldn’t consider using J-River though many find it a great option. I looked at using JRiver with a network streamer and the answer is No Problem – you communicate from J-River to your Streamer over the included DNLA porotocol. Which is a standard streaming protocol used by most if not all network streamers.