First off, you don't have to use any smart home stuff or AI to use this. It's really not that different from Heos, BT or Musicast. An advantage is you're not locked in a manufacturer's ecosystem.
The apps you use already have a Chromecast casting button/icon. It looks like this
. From a user POV it's not going to be much different than listening to Pandora through BT. Which you can also do with the Wiim.
The difference is instead of a signal coming from your phone, Chromecast facilitates the Wiim to connect whatever you're playing on Pandora to get the signal directly from your Wi-Fi. Your phone is just a remote at this point.
The advantage is a very stable connection that has nothing to do with what you're doing on your phone. Once playing, and your phone will show you what's playing, you can even turn off your phone and it keeps playing. Also, if you bought another AVR or stereo it might have Chromecast built-in or AirPlay, or you can add another Wiim type device and stream to multiple rooms in your house. Then you'll have multi-room audio.
I would use a Toslink cable like this,
Amazon.com: Amazon Basics Toslink Digital Optical Audio Cable, Multi-Channel, for Audio System, Sound Bar, Home Theatre, Gold-Plated Connectors, 3.3 Feet, Black : Electronics
and connect it from the SPDIF out (optical) from the Wiim to the Optical In #2 (Media Play) on the back of your AVR. Similarly, you could use RCA cable and go to Audio In #2 Media Player. On my Denin you can rename this input to whatever you want.