I believe all MacBook Pros since 2006 have digital output using a combined analogue/digital 3.5mm plug. It is optical though, so assuming you have a TOSLINK optical input, a 3.5mm to TOSLINK cable or a cable with adaptor such as the Belkin Digital Optical Audio Cable with 3.5mm Adapter (2m) would do it.

I think later MacBook Pros go to 94/24 on the optical output, but earlier models may only go to 44.1/16 or possibly 48/24 (I don't know).

(Probably not what you want if using Amarra, but if you were happy being fixed at 44.1/16 or 48/16 then AirPort Express or Apple TV respectively may be worth a look as a wireless solution.)

priorities: stereo music (primarily 'classical' / choral / opera)
boxes: various 500-series, DACs, G91 (+ non-M e.g. ELS-63)