I'm still a bit in the dark regarding how xspf may work w/ external audio. Per the following thread (http://groups.drupal.org/node/8757#comments), it seems like some sort of FeedAPI/EmField/XSPF playlist combo could do the trick? Also not sure if XSPF and/or MediaMover could come into play with Amazon API to generate audio nodes (http://drupal.org/node/241344#comment-798016).

Could be totally off, but this type of functionality would be great!