A replacement dual LNBF is about the same price, or even less than a 4x4 switch. A dual LNBF will give you independant reception on both boxes.
A local store here has the DMSI JSC322 0.3 dBdual LNBF for $20.00, but a Zinwell 4x4 multi-switch is $28.99, so it is cheaper to just replace the LNBF itself. You will have to run a second coax line to your second receiver.