I don't use iTunes except when I really have to so I had never heard of an iMix until I read your topic.
I must admit that its kind of hokey.
Once you have your music released by a digital distributor and its available on iTunes, you will be able to display the Apple page on your own website using an iFrame like this.....
http://web.me.com/roddymckay/Web-Media-Test/iTunes.html
As far as getting music to play on a website is concerned, were kind of stuck in limbo at the moment due to the fact that, up until recently, the best way was flash as this is the most popular browser plugin.
iOS devices like iPhone/iPad don't support flash so we really need to cater for these users by providing an HTML5 version.
Its kind of futile to drag a music file onto the iWeb page and depend on the viewer having or downloading the QuickTime plugin. A huge percentage of PC users don't have it and most of those in the corporate and educational environments are not allowed to download it.
I'm in the process of updating the iWeb for Musicians Music Player section to try to keep pace with all this. One of the things I am working on is implementing the new JW Longtail Video player for audio. Here's an example on this test page.....
http://web.me.com/roddymckay/JW-Player/JWAudio2.html