Apple Music not AM radio. To be clear, the difference is not the compression, since it's well established that at 320kbps, most codec are almost indistinguishable from lossless, but the whole sound signature is just different. Since Apple is usually tight lipped about their process, I spent a week doing A/B test and look for information, but can only speculate that either Apple's compression tool is better, or that they are using a superior master than Spotify. It's also not some Apple hardware magic, I'm using Android and Windows and can reproduce the results in addition to Sonos.