Doug,
In what way? Do you mean use an external audio for things like in-queue audio? (For example, many retail chains have an in-store "radio station" which they also use for callers waiting in queue.)
If this is what you are looking for, you need to use an "External Audio Source". This is a small executable (on the install ISO, I believe) you install on a machine with an audio card that takes the analog input and makes it available for use in Attendant.
Alternatively, could you clarify what it is you are trying to do?
HTH