you should be able to do this quite easily with
JACK, with one small caveat: amarok (last I checked) doesn't support JACK. You'd have to use a different audio player, like XMMS.
What is JACK? Its a low-latency audio server. It should allow you to redirect the sound output to the input device. I would suggest using the gui frontend called "qjacktcl" (that spelling may be off) or something similar.