Which ADCs were you planning on using? I believe that most of the serial ones use either SPI or I²C rather than what would be considered as typical computer "serial" (RS232). I would be very surprised if you could find one that would communicate directly with the differential RS422 port on a Macintosh, so you'd need to do some level conversion at least. A small µC might give you more flexibility than a standalone ADC, and a lot of them have at least one ADC built in, but you'd need to have programming hardware, etc, to get a program on to it – ask at your college, I'm sure they have something.