MacOS has a nice built-in feature called IAC (Inter-app Communication) that allows you to connect MIDI applications together and communicate with each other. (There’s nothing built into Windows but there are third-party applications like virtualMIDI that do the same kind of thing.)
However, there is no out-of-the-box mechanism to allow audio to be shared like this. So what do you do if you have a great audio application that you’d like to use with Gig Performer but that application doesn’t exist in a plugin format that can be loaded directly into Gig Performer?
Turns out there are several solutions out there. Click this article to learn more: https://gigperformer.com/using-loopback-to-send-audio-from-one-application-to-another/
Additionally, see this YouTube video: How To Send Audio From Gig Performer To Logic Using Loopback On Mac.