Is it possible to make voices unrecognizable in Audition 6.0.
Depends what you mean by 'unrecognisable'...
If you mean disguise the identity of the person, generally a pitch shift without altering the duration will do it. Up if it's a male, down if it's a female - well, generally that's true, but there might be exceptions!
The Chorus and Flanging effects can also be useful in disguising voices.