That's a shame - there isn't a Mac version of Audition 3. You need a creative cloud subscription, and the latest version (Audition CC) for that, or alternatively you can still purchase CS6, if you don't mind the version before, and no updates to it. You can't purchase the latest version - you can only rent it via the CC subscription.
Audition officially joined the CS series at CS5.5 (and had been re-written to run on Macs as well as PC at the same time). However, while the Creative Suite was up to 5.5, it was the 4th version of Audition...and CS6 represents the 5th version of Audition.
Audition 3 sometimes gets referred to with a CS number but it wasn't truly part of the Creative Suite. At that point, Adobe was providing Soundbooth for audio post duties alongside Premiere.
Confusing enough for you? Try being a long term user who remembers Cool Edit 2 becoming Adobe Audition 1!
In any case AA3 (which is what the OP has) was the last full version of Audition to run on PCs only.
That makes sense. In CS 3 and CS4 I was using Soundbooth, When I got CS5 it had Soundbooth, but then CS5.5 came out and it was replaced with Audition. I remember using Cool Edit 1 and 2 as well as Audacity and CD Spin Doctor for my MP3 editing before the days of Soundbooth or Audition.