Most computers built in audio is very "noisy". Computer produce a lot of interference and it's tough to get a good clean signal from inside the computer.
That's why most professional stuff has the audio device outside the computer and connected via USB.
The other problem is RCA and 3.5mm cables aren't designed to be used at more than about 9ft/3m. If they are longer than that they start to pick up interference from radio.
I'd recommend an audio interface and short as possible cables.
I think the best inexpensive one is the Presonus Audiobox: https://amazon.com/PreSonus-AudioBox-USB-25th-Anniversary/dp/B08D8R6VFC/
Just bought this (https://www.amazon.co.uk/gp/product/B08CXHFWS1/ref=ppx\_yo\_dt\_b\_asin\_title\_o00\_s00?ie=UTF8&psc=1) and fingers crossed it'll solve the problem by routing audio via the USB socket (assuming it's the 3.5mm audio output sockets which are the problem?)
Manual, Page 11 Explains each one.
Each playback device is essentially each channel on the GoXLR. If you want an app to go to the "chat" channel, you would set it's playback device to be "chat". To set an apps playback device, you can either do it some apps, such as discord and certain games or manually do it windows. Page 19 of that manual explains that. Or you could use a 3rd party windows app called ear trumpet that makes it super easy to change an apps playback device on the fly. Also lets you set the volume of individuals apps like you could back in Win, it is great.
For the recording devices, its seems that Broadcast Stream Mix, is for what ever is going to the device, beside the chat mic, such as audio from a game console, or if you have something like a ipod playing sound. The chat device is for your headset or XLR mic, and sample I belive is for any interal sound effects on the GoXLR - not 100% on that one.