You can’t send a DAW channel into the Ext In, that’s not an Output inside Overbridge. But you can bring audio that’s going into the Ext In on the A4/K into your DAW. So if your soundcard supports multiple outs then you could send a channel out via your card, into the A4/K Ext In and then back into your DAW.
Well, I have this Heat thing laying about here so i just wired those outs into my AK 
Sounds pretty good to me!
Not sure if I really feel the fx side yet tbh, was really hoping for it to be more flexible. But hardware knows its limitations, glad I’m starting to get a better understanding of the signal flow in the AK. Thanks again!