OMS is also freely available (Open Midi System). Apple MIDI Manager runs best on older System software (7.x.x and below). There's nothing wrong with a 61xx if you're running a stable System (7.6.1 or 8.1 - 9.1) with enough RAM.
The 5 pin DIN plug (of which only 3 pins are used) is a MIDI plug. The 8 pin Mini-DIN serial socket on the Mac does require a Mac serial (not USB) MIDI adapter to connect to MIDI equipment. There are several discussions here on this subject, which you would have discovered had you searched. You should be able to pick up a simple one in one out MIDI adapter for next to nothing on ebay.
The 5 pin DIN plug (of which only 3 pins are used) is a MIDI plug. The 8 pin Mini-DIN serial socket on the Mac does require a Mac serial (not USB) MIDI adapter to connect to MIDI equipment. There are several discussions here on this subject, which you would have discovered had you searched. You should be able to pick up a simple one in one out MIDI adapter for next to nothing on ebay.