The Twin only directly supports 2 receivers, so you would need to add a switch or replace the Twin with a DP Quad.
What receivers do you have now? You could replace one of them with a dual-tuner/dual-output model. That would require either adding a DP34 switch or replacing the DP Twin with a DishPro Plus Twin. If you connect the receiver to a phone line, the addl outlet fee is waived and you can have 3 rooms for the price of 2.