The only cascade solutions I'm aware of use the xx21 switch downstream from another multi-sat switch in order to add one more satellite.
The DP21 passes just one of its inputs to its output. If you used one to feed say 61.5 and 77 to the 1000.2's input, and you have a receiver viewing 61.5, what happens when another receiver wants 77?
You might be able to run a 4th satellite into the 1k2 input, then add a DP21 to a 1k2 output to add the 5th. The DP21 is not a Plus switch so if this is for a dual-tuner receiver it will take 2 out the receiver outputs with 2 runs of RG6 and 2 DP21s. Has anyone tried a 1000.2/DP21 cascade for 5 satellites?