Linear encoder outputs

Greetings All

Does anybody have an answer to the following problem. I have recently
purchased some Acu-rite Turnmate scales which I intend to fit to my
lathe and milling machine. They are about 10 years old but are brand
new and still in their sealed packaging. My idea is to connect the
outputs of the scales into the serial or parallel port on a PC to act
as a DRO(I already have the software for this). The output of the
scales is analogue differential sinusoidal quadrature phase current at
7-18.5 micro amps into a 1Kohm load, but I need the usual 5v quad phase
TTL signal for the computer. Does anybody know of a circuit I can build
to effect this conversion?

Best regards

Phil Sumser
New Zealand