Your 1000.2 will only support 3 dual tuner receivers without switch help.
Adding a DPP44 and cascading a DP34 off of that will get you four new connections that will support two more dual tuner receivers, each with two lines run to it (DP34 cannot band stack).
Not an inexpensive mod, the DPP44 will run ~$200, plus receivers plus DP34.