Digital Advice

I would recommend Node - my rationale is it’s a streamer/DAC. You could connect your Mac to it and I found streaming to be a lot more convenient that sifting through my computer for files. 
 

I also prefer streaming DAC for simplicity. 

Check out the BlueSound Node N130 or newer. It streams Amazon and does great things for little money. New or used.

All the best.

Use your Mac to stream to Schiit via USB. This will beat WiiM and Bluesound. 

I'm not sure. I had been streaming from my Mac to a DAC for a long time before switching to dedicated streamers. I would suggest streaming from a Wiim to a good DAC instead. The weak link in both the Wiim Pro+ and Ultra is their internal DAC, but the RC and PEQ (with a good mic and proper setup) compensate for it, making them almost indispensable yet very affordable hi-fi gear.

The Blusound node can be bought for a couple hundred on the used market. The app is the best. I don't think there is a better low cost solution. I don't know if $600 elevates you much. 

Without going overboard - audphile1 has a solid suggestion. You might consider a new Schiit Miodi instead of the used Bifrost. It has a nice USB implementation that will isolate the DAC frrom your Mac.

https://www.schiit.com/products/modi-plus