Simple MBOX and PTools problem.

Hi there

I have borrowed an mbox from friend to do some editing away from my studio.

I do not have any monitors set up where i am and no headphone either to connect to the mbox.

i was hoping i could set my output to built in output on the AMS (I am running macbook pro) but there seems to be no sound when i open pro tools up.

i only have the option of output 1 and 2 on master fader to output.

i take it what i want to do is not possible as you have to input / output through pro tools interface etc???
thanks for any help.