I can't see why you would loose any fidelity. The WiiM is picking up the stream and sending the digital info to the amp. and you're using the R-N800's DAC.I'm able to Chromecast to the WiiM via wifi, and the WiiM confirms a 24/192 signal going to the Yamaha via coaxial cable. Do you think I'm losing much fidelity by having that extra link in the chain? I'm loathe to switch to an IPhone.
If I switch streaming services, do I have to make an all new library and playlists, or will one of them import from Apple Music? I'm no Apple devotee, but I am lazy. LOL.
Libraries and playlists are specific to each service and your account with that particular service.
The 24 bit Ultra Hi Res concept is IMHO somewhat of a scam anyway (so that streaming services can just charge more for their product). Well recorded, mixed and mastered content sounds fabulous in 16 bit CD quality. A lot of modern 'popular' music is so badly mastered (due to the loudness wars) that it often seems to sound worse in 24 bit.
Unless you have an ultra expensive system in a treated listening room and are listening to well produced material the average joe is not going to hear any difference.