Squeak,
I have the Universal Sound Card Midi Connector Cable you initially asked for. This cable connects your midi keyboard to your computer's sound card's joystick port and as was explained earlier still has a thru port to connect a joystick if you play games. this cable sells for $20.00 for 6feet and $24.00 for 12 feet. There are two midi ends, one for in and one for out and the 15 pin joystick connector on the other end.
You could also use the to host port on the 550 but most of my customers use the universal sound card. The only advantage of the to host port would be if you didn't have a sound card with joy stick port (laptop computer).
George Kaye
Kaye's Music Scene
Reseda, California