Yes, you need a Ku lnb for X4.
primestar dish will work fine - that's what I have.
Most of the original primestar LNBFs have 2 separate outs - 1 for H, 1 for V polarity. You could use 2 cables to the 920. Or you can replace the LNB with one that has polarity switching by 13V/18V.
I found an...