Cthulhu and Digital Performer

I can not find a way to make it work in Digital Performer& Please help!
How to route the MIDI From Cthulhu to the Instrument thru IAC Driver?

From a user post in the Cthulhu user forum:

First, after having set up IAC in the Audio-MIDI setup, enable Multirecord-which is the way you can direct a specific input to your synth plug-in.

Load Cthulhu as an instrument track, and make sure it's detected your IAC bus.

Assign your controller as an input to the Cthulhu track.

Load your target AU/VST synth, and assign IAC as an input.

You'll need to enable recording for the Cthulhu track and your target synth. Both will record data, the Cthulhu track only records the single note you trigger, but the target synth will record the chords that Cthulhu dishes out. You can erase the single-note data on the Cthulhu track when you are done recording, or simply click the blue play-enable button, in case you want to go in and edit the single-note data for later use.

These instructions aren't so helpful. what does "set up IAC" mean. It's just a weird window with "add" and "delete" buttons and no hints as to what they mean or due.

The add and delete buttons are used to manage multiple named IAC busses. You just need to add one for this purpose.

https://help.ableton.com/hc/en-us/articles/209774225-How-to-setup-a-virtual-MIDI-bus

The I and the A stand for Inter Application. They let you send MIDI between different applications on your machine.