Apples and oranges. One (midi) is data, the other is ONE means of transmitting that data. The good news is that once you figure it out, you shouldn't have any trouble syncing it up. Maybe Bachus or Abacus or someone with more patience than me can lay it out for you.
chas
Its what Chas says, usb uses the same midi data as the physical midi cable.. its just a different type of cable..
And audio is still audio.. you connect the audio out of the pa4x to the audio in of your computefs audio interface..
Keep in mind tough that after installing the drivers, you will need to configure your midi interface and audio interface in protools to.
But once you are set up, the workflow is not really so much different as on your dp24, which is a brilliant machine. But the end quallity may be much better as pro tools lifts the final audio and dsp quallity by quite a considerable margin.