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There are lots of ways to connect things together.
Please tell us about your signal chain. Do you have T1, T4S or T8S ToneMatch mixers or something else?
If you Behringer mixer has a monitor or aux send, then create you monitor mix and send that to the L1 systems. Then send the main mix to the F1 Model 812 systems.
If the Behringer mixer does not have monitor or aux send, then you can connect the mixer main outputs to the F1 Model 812 systems. Then run a line out from each F1 Model 812 to the L1 systems.
You can daisy chain from the F1 Model 812 systems to the L1 systems, but not the other way around.