The XITEL MD-Port DG1 works fine (and is 100% digital) with the Macintosh.
Requirements:
Mac OS 9.0.4 (I have not tried it with Mac OSX Beta).
USB (I have an 8500 with a OrangeMicro USB/Firewire PCI card and Sonnet G4 upgrade.)
Music Player (SoundJam, Audion, MusicMatch, etc.)