Well I see that no one has answered your question, so I have been looking through all of the documentation and especially "change system feature" and found nothing that suggest that u can change the bit rate.
If nothing else u could call AVaya in denver and if u don't have maintenance,before they have a chance to ask for your customer id or anything, ask them your question.
I have worked on Intuity for over 5 years,and never seen any place that u can change the bit rate, so beings how DEfinity audix is the poor mans' version of Intuity, I would say it is unlikely that u can change it.
Do u want better fidelity on the recording? What problem are u having that u want to change it?