Yes, use the Multichannel Encoder in Auditions Multitrack View.
However, you can not import a Project from PPro and then export the audio from Audition. You have to manually import each audio file into a Multitrack Session in Audition and then export the audio. So it may not be the best solution...
EDIT:
You will NOT get any Dolby Digital (.ac3) from Audition's Multichannel Encoder. Sorry if i mislead you...