Files created by Gig Performer can be opened by both macOS and Windows computers. If the computer you're using to access the file is missing some of the plugins that were present when the original file was created, Gig Performer will create a "chameleon" plugin that mimics all the properties of the original plugin except the actual processing. This will allow you to modify the file, save it and later re-open it on a computer that has all required plugins installed.
Similarly, if the audio interface connected to the current system does not have enough inputs or outputs to accommodate the setup utilized by the file, Gig Performer will prompt you to create "Virtual channels" that produce no input or output but retain all connections. Doing so will allow you to modify the file, save it and later reopen it on a computer that is connected to the original audio interface.
If you plan to use Gig Performer on both macOS and Windows, you may want to consider just using VST plugins on macOS rather than AU plugins. This will make it easier for you to use the same gigs on both platforms, assuming of course you have the plugins themselves on both platforms.
For more information, please refer to this blog article Cross-platform usage and moving from one platform to another.