What Broadcast Warehouse have done is effectively bridge the vast gap between the really low end kits out there and the expensive Professional gear, using appropriate engineering compromises to greatly improve performance while still reining in costs. It appears that using PICs instead of lots of hardware is one of the hallmarks of Broadcast Warehouse products. Programming PICs need a different skill set than just bringing together chips for a hardware implementation. The resultant final products are cheaper, easier to modify and customize and use less PCB real estate. Slower switches would generate more intermodulation distortion products due to larger ON and OFF times.
Lets begin from the beginning.
That is followed by a passive 15 KHz LPF brickwall filter. The next stage is a clipper. Outputs from the Left and Right channel clippers are fed to the DG411 switch that TDMs the signal. The Pilot tone is added to the output of the TDM using low noise Opamps. This MPX signal is then fed to a passive MPX filter.