@Charlesh214
The DM64 Mix Rack is the mixer, so the 2x C3500’s are controlling the same mixer.
A multi-surface setup like this can be setup and used in many different ways, but it might be that you are accessing (for example) half the input and output channels on each surface.
You could therefore do something similar with the FX, by just ensuring FOH uses FX 1-8 and Broadcast uses FX 9-16.
Unless by ‘FX’ you mean the channel processing?
In which case, you may need more in depth assistance with the whole setup, so I’d recommend getting the installers/integrators back in to finish the job!
(you can also contact us directly via support.allen-heath.com)
Thanks,
Keith.