To your questions:
- Probably not. Your speed is fine for audio streaming. Not sure what is causing your "digital artifacts" but probably not the speed.
- Having the router near your hifi system is not necessarily a benefit, but hardwiring the streamer is a good thing so overall a win.
- Yes, hard wiring your streamer to a wifi extender/booster is a viable option, but better would be hard wiring from a mesh system satellite, and best is typically considered to be hard wiring from your main router base unit to your streamer. Whether either of those options is better than another can be system dependent, and they all might work just fine for you.

