There are no third-party integrations with Apple Music so if you go the separate streamer route, you’ll need to use AirPlay which is stuck at 24 bit / 48 kHz max for AirPlay 2.
You can play back high-res files from Apple Music on your Mac. You just need to enable it from the Music app. Go to Preferences -> Playback and then select the highest resolution from the ’Streaming’ and ’Download’ dropdowns.
You’re on the right track as far as audio quality and streamers go. They’re all 1’s and 0’s. As long as the data is getting to your McIntosh DAC intact, then one streamer is no better than another in terms of audio quality.
There can be wide variations in terms of ease of use, features and technical support so I encourage you to make your choice based on those criteria rather than on anecdotes on sound quality.
A streamer is basically a computer with some specially configured audio software. For example, I’ve made my Mac mini into a streamer using a free app called Kodi. I also have a Raspberry Pi based streamer running moOde for my basement system. I’ve got a fairly technical background so I went the DIY route. You might view the Mac as a temporary situation or are less technically inclined which nudges you towards a turnkey solution.