I’m not sure I can notice the difference

There are three qualities, in my simple view, the normal mp3 / aac quality, CD quality and superior quality. For superior quality you need a dac somewhere. For cd quality you need wired headphones or, I assume, a jack that terminates in rca for your amp.
you can stream and download cd/superior quality from Apple. As I understand it if you blue tooth cd quality to your amp that’s lossy (blue tooth has limited bandwidth) so no point having cd quality.
Overall it’s a good next step forward and means the average joe like me can have 60,000,000 cd quality tracks within my monthly subscription (over wired headphones). I’m in a sweet spot because my iThingies are new enough to take iOS 14.6 but old enough to have 3.5mm jacks. I believe Spotify , Amazon are following the lead.