I would say that the p39a0 is not a bios chip. It is in the same area as a chip that is on several other versions of motherboards. I would have to say that the Xyclops is the bios/eeprom/pic chip.
I wonder if there are going to be many more revisions in the near future. If M$ is going to release a new "smaller" version of the xbox, this v1.6 could be in preperation for that. It is possible that they are releasing newer motherboards, with electronically compact designs that could easily be compacted. That way they actually have the same parts on both the standard xbox and the compact one, which would save alot of money. This could also be the reason for the disappearing memory spaces.
Now we just need to wait and see what people make of this. It will be interesting.
KingViper