Is there a multiswitch on the back of the Phase II dish?
Why are you upgrading to a 5x8 switch? With two DVRs you only need four lines with the attached switch on the PH II dish.
If for more than four outputs, you have two ways to do it. 1) disconnect the attached switch and connect the lines from the LNBs to the same inputs on the 5x8. or 2) attach the four lines from the attached switch to the four sat inputs on the 5x8. Power is supplied using another coax connected to the power supply.
As this person said, he or she has a Phase II dish. A Phase II dish has a built in 4x4 multiswitch that resides in the three lnb adapter at the end of a lnb arm.
It automatically has four outputs that can be used to go to two DirecTivo's, with two outputs going to each DirecTivo. I haven't seen a PhaseII lnb in a long time, but as I recall, if you remove the vertical through stove bolt that holds the adapter to the lnb arm, you will see four cables. These are the switch outputs to which you need to connect the receivers.
I know for sure of one 4x8 multiswitch that will work with a Phase II dish, in case you need more than four outputs. That switch is the Zinwell SAM4803.
Forget the Terk 5x8. I know for sure that the Zinwell SAM4803 4x8 works with the Phase II dish. It is the only one that I install, since I've had quite a few problems with the Terk when it comes to Phase I and II dishes.
If you can't find one. IM me. I can do better than most online dealers, since I buy them in bulk and install them, too. You can have it by Priority Mail in 2-3 days.