I spent _hours_ trying to softmod a friends v1.4 (v1.5?) Xbox after having done 2 others, one of which was (I believe) a 1.3. and the other a v1.2. It took me a lot of time, and a fair bit of panic when I mucked up a file so the Xbox wouldn't boot and had to hot-swap the hard-drive after booting a game on the semi-dead Xbox, and plugging it into my Xecuter-2 modded machine.
I've tried PBL 3.5i, 4.0 and 4.1 with X2 4981.06, 4979.06, 4977, & EvoX M7. All have the same result (Using debug RC4 Key and the 1.0/1.1 EEPROM keys in the boot.cfg). Phoenix loads fine (apart from the focus encoder issues in earlier PBLs), select the BIOS, the screen flickers a bit, then goes black and everything freezes. If the guys over at Gueux can get this working, then I'll be even more impressed than I am already, as I've spent a fair bit of time perusing forums trying to work out what's going on.
Does anyone know what actual changes there have been in the Retail BIOS's other than support for different video encoders? My own Xbox is a v1.1 and I can't detect any differences in functionality in the rare occassions when my machine has the chip turned off.