[robespierre]

There's a little 2-pin header labelled "NIC" in the corner of the board too; sometime in the next week or two I may stick a logic analyzer on it and see what I can see.  I have a working theory it's i2c just due to VOC & other major chips manufactured by Philips Semi, where I2C was big in the 90s.  (Though you'd need to pull a common ground from somewhere else; it's a little weird to not just put a ground pin in the same location)

No, it's 1-Wire. The second pin is the ground pin.