Mach 5 can work either as a RTAS or HD/TDM plug-in. First create an audio Track and call up the Mach5 as an insert plug-in on that track. You must do this as the first step as the Mach5 will not be available as a source for MIDI information until it is instantiated on an audio or aux track.
Second, create a MIDI track in ProTools and click on the MIDI tracks output. You will see the Mach 5 we just created and any other instances of a Mach 5 that you have in this session. highlight the Mach5 option and then you will get a drop-down menu that specifies all of the MIDI channels of that particular Mach5. Choose the MIDI channel that the sound in the Mach5 is assigned to.
You can now record enable the MIDI track. When you input MIDI into this track, you will have sound.