Can anybody tell me where the amarok config file is that holds information on which backend is in use by amarok. ie gstreamer, xine etc.

I switched the backend to gstreamer from within the amarok program but now amarok won't start due to a gstreamer problem.. so I can't get into amarok to switch back to xine.

I therefore need to know how to change the backend Amarok is using from the command line.

I'm running opensuse 11.4 (KDE)

Any help will be really appreciated. Thanks.

Amarok shares/uses the same kcm module as systemsettings

systemsettings -> hardware -> multimedia -> phonon -> backend

But please do not use the xine backend, it is obsolete and unmaintained. The currently maintained backends are the gstreamer and the vlc backend.
If you change the backend within the Amarok settings, make sure you don't have music playing and restart Amarok to initialize the backend.