Disklavier

Newbie here:

I have a C7 with DCK 500 R XG.  

I also have  the adapter cable (MIDI to USB), Yamaha UX 16

And my iMac G5 (OS 10.4)

My software:  Sibelius 5 First.

All hooked up....but I don't think I have the DCL itself correctly configured.  The  manual is 
confusing to me.

I can "read" (pick up the icon) of the UX 16 cable in my computer (in both the Sibelius and 
the utility, Audio Midi set up. So, every thing from the cable to the iMac is fine, I believe.

But unable to use the C7.

I am very new at this.  Have had this piano for 5 years, but really havn't taken the time 
until now to learn how to use with my computer.

Any help out  there?

thank you!

Jon Mutchler

PS:  I am trying to write and play back piano music using the C7 and iMac.  That's the end 
game.