wont work because it will only get one polarity
On the 5th reciever, do you want only 91? If so...get a simple multiswitch (a DirecTv 3x4 works good)
Hook that to the 2 outputs of the 91 LNB
hook your 2 lines that are there right now (that go to the switch) into 2 of the outputs of the new switch
run a new cable from the switch to 5th receiver
so it would be setup as such
91 LNB out 1----3x4 multiswitch-------SW44 switch--------------receiver 1
91 LNB out 2----3x4 multiswitch-------SW44 switch--------------receiver 2
--------------------3x4 multiswitch----------------------------------------receiver 5
82 LNB out 1-------------------------------SW44 switch--------------receiver 3
82 LNB out 2-------------------------------SW44 switch--------------receiver 4
all get both satellites except for receiver 5 that only gets 91