I'm not sure what you are trying to do.
I think of the IAC like another MIDI interface - but only in software - where you define MIDI busses so you can send MIDI to/from applications running on your computer. With the IAC driver defined in Audio/Midi setup, you could create an IAC buss and, e.g., and send MIDI to it from a track in Logic. Then you could set some other application to receive that MIDI data from Logic via the same IAC buss (or vice-versa). The IAC buss can be a more flexible way to route MIDI between applications compared to using Rewire - where one application has to be the master and the other as to be the slave. I've read that there may be some latency issues with using the IAC buss though.
It can be useful to think of tracks in Logic as just containers for audio and MIDI data (objects). There's nothing hard coded to prevent putting MIDI regions on "audio" tracks and audio files (or regions) on "MIDI" tracks. But obviously it does not accomplish anything to playback audio on a track whose output is assigned to a MIDI instrument (or a MIDI port like an IAC buss). Similarly it does not accomplish anything to playback MIDI data on an audio track (even though you can record MIDI data there).
Maybe another example of how tracks are not fixed with respect to the data (or objects) they contain, is that Logic always has to route the MIDI data it is receiving (via the physical sequencer input object) somewhere, i.e., Logic will record incoming MIDI data on to the currently selected track - even if that track is assigned to "No Output" or it is an audio track (you don't even need to have the record button in the track header). Subsequently, if you want to playback MIDI that was recorded on the "No output" track, then you could either re-assign that track to another destination (a MIDI instrument), or you could just drag that MIDI region to an exiting MIDI instrument track. While this can be confusing, it is often one of the differences between Logic's "object oriented" design and other DAWs.