Does Amarok 2.0 support multiple audio backends, xine, gstreamer, etc?
Yes, but not the way Amarok 1 did. From now on Amarok only supports Phonon, which can in turn, use the aforementioned libraries. As a result the amount of supported media types will likely increase as more Phonon backends become available. To change the backend you should open KDE’s System Settings and choose Multimedia; in the Backend tab there is the list of installed backends from which the user can choose from. Changing the backend will affect all the applications using Phonon (mostly, but not limited to, KDE applications).