MIDI Connection Issue

I have a very nice Roland RD-600 keyboard. Though this is considered a dated model from over 10 years ago, it's still in very nice condition and hasn't been used very much. It's fully weighted, with 88 keys, and a large number of instruments. I have some MIDI cables as well as a Roland UM-2 Super MPU32 USB MIDI interface and would like to hook everything up to my Power Mac G5 to record with GarageBand '08.

I have a MIDI cable on the keyboard's MIDI out port. This same cable is connected to the UM-2's MIDI in port. The UM-2 is connected to the Power Mac via USB. However, the Audio MIDI Setup application doesn't recognize the keyboard and none of the lights on the UM-2 light up when I press a key on the Roland. From what I know of the connection, this should pretty much be a plug-and-play situation but of course, these things are always more complicated than they appear.

A few years ago, I managed to connect this very same setup to a Apple PowerBook with Finale '97 running and managed to at least use the Roland as an effective controller. I'm wondering whether the UM-2 isn't compatible with current USB standards for a Mac or whether I'm doing something else wrong. If anyone with experience with this kind of a setup could help, it would be greatly appreciated. Thank you in advance!