Well I can tell you in order to upgrade the device with a radio and ROM to do GPS you will need to look and read
here.
Over all, keep in mind you need Olipro 2.4 to unlock the phone. But before you do that you will need to be ready to do everything all at once. What I mean to say is once you unlock it you cannot stop there. You must then flash the Radio and then the ROM.
To do GPS on a xv6800 you need to unlock it using
Olipro 2.4 and then flash the Radio to something like
3.42.50 and then flash the ROM to something like 3.56 using
BuildOS.