This is such a limited protocol that could be done so many different ways.
First off all, if the user wants, they should be able to “sum” send multiple tracks out the ExternalFX output, just like they can any other output.
My tip for you is to create a Template, with pre-created External FX for your outboard, and then create Groups for each one, and name your groups in a recognizable way like “Ext- LA2A”
Secondly, when exporting… and you have an External FX plugin somewhere in your 1000 track project and you haven’t even been using it for days and can’t remember where it is… “Export Must Be Done in Real-Time” - NO! Give us the option to disable all External FX plugins!
But I highly suggest my workflow tip to you. Create External FX utility Group Channels that do nothing but send signal. Easier to find them and disable them, you can sum to them, you can use sends to them, you can set channel outputs to them, you can A/B easier, monitor pre Ext FX plugin or Post, etc, etc