If you are in need of combining audio channels from 2 different locations (stage and Mon mix) at the FoH mixing location, then a reverse FoH split setup as shown below can solve your problem. This FoH split setup also can be used to cover 2 sides of a large stage. For example 16x8 stage box at each side of a large stage can serve up to 16 mics. These 2 stage boxes can be connected to FoH splitter via single cat-5 thus combining 32 channels from stage at the FoH mixer. The returns (say 8 channels) from FoH mixer will be available at the both ends of stage box for Amplifiers and other purpose.
Combining multiple channels from 2 different locations at the FoH location
Combining multiple channels from 2 sides of a stage at the FoH location