If your older receiver has a coax/optical input, I would use those outputs on the Wiim to the receivers' input. The receivers DAC will do the conversion.
If not, just use the analog output on the Wiim to an analog "IN" on your receiver. The Wiim DAC will do the conversion.
What model receiver or amp/preamp do you have? That will help us give you the best option.
Since you also said you are new to streaming, have you chosen a hi-res service like Qobuz, Tidal, Amazon? Or will you use Spotify, YT Music, etc? If audio quality is important and your equipment is decent enough, hi-res or at least 16/44.1 CD-quality would be my recommendation.
The Wiim Pro has both Ethernet and WiFi options. I use wifi 5Ghz only and I have excellent signal and a 300Mb up/down. In the 9 months that I've owned the Pro, I have never lost connection nor have I had any pauses or buffering. Wifi, for me, has been flawless from Day 1.
I repurposed an older tablet with a 256GB MICRO SD card with WAV and FLAC files and the Pro sees that card and plays all of the files that are on it.
The Pro really is a great product with many capabilities. For me, it does everything that I expected from it and the Home app on my Pixel 8 Pro controls all of my settings and playback controls.