I use a MIDI Timepiece (original) by Mark of the Unicorn (MOTU). I think even the modern versions have an 8-pin serial port for older Macs. MOTU's own FreeMIDI software works good. The MIDI Timepiece is not a "dummy" interface - you can do a lot of complicated setups with it. And best of all, you can find them for a decent price on eBay.