I had the same problem...
I got the same cable, the UX16, and it's been driving me nuts. I have a P70 Yamaha keyboard and I can't get it to work with the cable and my powerbook. I've got OS X 10.4.7 and the cable stops support at 10.4.5. My Mac recognizes that there is a midi device, but then I can't get it to do anything with garageband. I would GREATLY appreciate any advice.
I experienced exactly the same thing (exception for de midi port witch is a Uno M-Audio). I was very frustrated...
I report the problem to my salesman and we tried (in the store) many other keyboards (on my ibook) to find that all other brand worked just fine and were perfectly recognized by Garagebang. It wa simply "plug and play" (witch is what I always expect from my Mac).
In fact, he had never seen that kind of midi troubles. So he went to his yamaha representative this week, who told him to forget about that. There is, according to that yamaha representative, a business conflict between Apple and Yamaha, and they dont provide Apple anymore whit the internal source code...!
Then I was furious!... They should have wrote on the box that the piano was'nt compatible whit Mac. It would have saved me a lot of time and frustration !
The good news is that I found on the net a strange receipe that worked just fine for me with Garageband (remember that I use a M-Audio Uno interface - I don't know if it will work with the ux16). Here is the quote
"The interface works fine. It`s really plug and play. The included software is really easy to install. In one minute you are connected.
I had a problem with my Yamaha P70 digital piano and Garageband. Garageband recognized wrong notes while I was pl... Read more >ayng. I solved the problem setting my Yamaha p70 in that way: dual voces at the same time (grand piano 1 and 2) and both +0 octaves, so the two voices are perfectly overlapped.
With this setting, Garageband is working fine, and recognize correclty the notes.
Be aware that this product may not work properly with your Yamaha keyboard. "
I dont know if it will wotk with other software and I'm thionking to maybe change my keyboard. Unfortunatly I just love it, so I dont exactly know what I'm going to do.
Let me Know if you hear something else and if this helped you.
Goood luck.