UI elements question

I'm trying to write a simple script that sets the default audio
output device to "Built-in Output." This is done by clicking
something in the Audio MIDI Setup application, so after some fiddling
to figure out what ui element was what, I tried the following script:


tell application "Audio MIDI Setup"
activate
end tell

tell application "System Events"
tell process "Audio MIDI Setup"
tell window 1
tell tab group 1
tell pop up button 6
set value to "Built-in Output"
end tell
end tell
end tell
end tell
end tell


This script activates the Audio MIDI Setup application but
unfortunately, it has no effect on the selected value of
the default output. I guess the general question is how do
you set the value in a pop up button.

Any ideas?