Cable adapter for Subaru CD player to radio/cassette

I recently purchased the CD player add-on that fits into the unused bay in my Outback console. There is a cable that should connect the player to the existing radio/cassette but the plugs don't look at all alike. The one from the CD player is a "DIN" type (round) while the socket on the radio is rectangular. Does anyone know of an adapter from one to the other or a reliable conversion scheme or am I SOL? W