Does your Sansui have a "phono" input? If not you will need an adapter box. YOur turntable should have RCA type plugs which would look like they could plug in to any right and left input on the back of the stereo, but it has to be a Phono input. Radio shack may still have the adapter boxes, I am pretty sure NAD still makes one too.
May cost 100.00 or more. If you need this box, once you have it you should be able to plug into an "AUX" input on the stereo.
As for transfering to your Mac.. that will depend on the type of inputs you have on the Mac. You should be able to turn your stereo on to Phono or Aux depending on which route you have to take, then turn on the Tape moniter, have a set of audio cables coming out from the tape out, going into an audio input on your Mac. This input card will have to accept analoge not digital. You may also need a stereo rca to 1/8th mini adapter, as many cards on computers use 1/8" mini jacks . Hope this helps and good luck