Be interested to know exactly how you did that. I have been trying (unsuccessfully) to upgrade to PDXIB1 as well.
Now tried going straight to this pre-release but keep getting "Emergency Mode - You must push detect button...before you connect the USB port". I have hit detect but as soon as the phone switches on Mirage simply says "PDA device not found".
I haven't got an XP machine and cannot download XP mode. I can run Vista or Win 7. I haven't found usb drivers for Win 7. I assume this is the problem.
I really want to get rid of the Orange branding (as the phone is now out of contract) so any help would be greatly appreciated. TVM.
Galaxy i9100 - CM10.1, CM9.1, dorimanx 8.1 (dual boot)
Galaxy i9000 - CM10.1, CyanCore 2.4.1
Galaxy Tab 2 - CM10.1, DhollmenCM