DEFINE SHIFT_PAUSEUS xx where xx is some number will slow down the SDI transmission. Looking at the data sheet, it shouldn't be necessary but maybe worth a try? No harm in trying to make up one 16 bit word for transmission either, maybe that would help.

Like I said, I'm pretty new to PICs but I've found if I thrash around and change enough stuff I can mostly get stuff to work....mostly.

As far as I can see, your connections and logic look good. Sorry I can't find you a magic bullet.