Currently, you cannot use Reaktor to process audio in realtime with ProTools. This is because Reaktor can only communicate to ProTools using DirectConnect. DirectConnect was designed by Digidesign for ProTools to receive audio from another application, but does not allow for ProTools to SEND audio to another application. In order to use Reaktor to process audio from your ProTools session, you will need to find the audio files for that audio track, and load then into Reaktor directly, process them, and then bounce that audio out. You can then load that processed audio track back into your ProTools session.