Logic Pro X 2 audio interfaces via aggregate in Logic X but only 8 visible from one interface!!


Tying to resolve why I can't see my second audio interface Zoom tac 8 in Logic X.
I've assigned them both together successfully with aggregate, but don't see how you configure to use 16 tracks from both units.
I can only see 8 channels of the one of the interfaces in Logic and don't understand how to see the other to follow on from track 9 to 16.
I'm surely missing something here having this being my first time in using two interfaces.
Any help would be gratefully appreciated...as I'm completely stuck at the moment.