In Qlab,
WORKSPACE PREFERENCES / AUDIO tab
Drag a wire from the first patch point to your UAD.
Assuming the drivers are installed for the UAD & your Pro Audio license is active on that machine, you should now be able to send any audio cues you have to 1 thru 8 by turning up the level (under the levels tab) of each cue.
You shouldn't need to mess with any of the audio / midi settings in the OS unless you also want things like Itunes to play thru your UAD. Even so, you still have to do the patching in QLab mentioned already.
ra byn