I don't often agree with Dre, but his point is valid - O2 failure does NOT explain the repeated course changes the aircraft made - and if a hypoxic pilot somehow managed to program all that in the computer before passing out - why would he input that course (which conveniently skirts around ground radar coverage).
My personal favorite theory is that it was some sort of planned hijack/hostage taking (or kidnapping) plan that went wrong. One pilot intentionally depressurized the aircraft to keep the passengers from making a ruckus, overdid it, and when he realized everyone was dead, he pointed the aircraft towards the most remote bit of ocean he could come up with, and then turned off his own O2.
But like all the others, it's just a theory at this point.
BTW, if the black boxes are ever found (and are still functional), I seriously doubt the CVR will have anything useful left - it was so long after whatever was the initiating event that any info would have been written over. The FDR would be the best hope.