I have 2 mini’s as well. It’s where I started and got hooked to Wiim and its whole value offering.
The difference between the products is their dac offerings…mini + pro vs plus vs. ultra. I hear a small but meaningful difference between the mini and plus. Never heard an ultra but am told the difference is even smaller. So no surprise you hear no difference between them. The key is that you enjoy them all and your music!
I have very little experience with Amazon as I am a huge YouTube Music user. I tried high res on Qobuz for a month and really could not hear a difference. Moreover less than @0% of all tracks on high rez sites are true hi rez.
I have zero problems with YouTube Connect and no one completes with the size of their music & video library. As a music lover, its most important to me. We also enjoy ad free YouTube video’s on TV…we watch a lot of YT content. All for $13.99 / month…such a deal!