The Emagic Unitor8 USB midi interfaces were expensive, but worth every cent. Mine was over $700 when I bought it. They were the top of the line with ultra low latency, and are extremely well built. Nowadays you can Get a similar USB midi interface for much less money, but still very few offer the internal routing, device chaining, and filtering features that the Unitor8 or AMT8 offer.
Many Unitor/AMT 8’s are still running strong after 10 years of hard use! I know mine is, and I have no intention of replacing it. But since Apple acquired Emagic in 2002 they have abandoned writing a decent, non-crashing, well tested, modern (ie: for leopard), configuration application for them. Considering the fact that Apple itself now owns the rights to the interface, I don’t feel there is any good reason for this situation. It’s not a difficult task, especially given Apple’s resources. On the other hand, They have maintained the usb drivers for the interface and do provide a version compiled for their latest Intel based OS X machines, and it can be installed from the Logic 8 discs, and from Garageband. This makes it the only midi interface to have specific drivers written by Apple.