Flashing the BIOS
Version 2.40 is the latest Cromwell BIOS, but my DuoX 2 came with 2.32. So the first thing I wanted to do was flash it to the latest version using HTTP. I first plugged the Xbox into my LAN and then connected it up to my television.
I next downloaded the latest version of the Cromwell BIOS from SourceForge. The download includes two versions - 256 kB and 1024 kB. But unfortunately, the DUOX-2 mod chip has 512 kB banks, so the 256 kB version needs to be padded out to 512 kB before it can be loaded.
To do this, download the excellent EVTool and the 256 kB version of the latest Cromwell BIOS. Then, extract cromwell.bin from the downloaded tarball, which should be roughly 256 kB. Next, launch EVTool and make sure the 512 kB radio button is selected. Then click on the Size... button, select the cromwell.bin file that you just extracted and then save it to cromwell512.bin.
Figure 7: EVTool
(click image to enlarge)
In order to flash the DuoX with this new firmware, you'll need to boot from the other BIOS (called FlashBios). So turn off the Xbox, switch the modchip to bank 1 and turn the Xbox back on. If all goes well, you should boot to a screen like the one shown in Figure 8.
Figure 8: FlashBIOS boot screen
Now, leaving the Xbox powered, switch the mod chip switch back to bank 0 so that the Cromwell BIOS is selected for flashing. At this point, you will need to navigate through the menus. The game pad that came with my machine was no help for navigation and I have read that only official MS gamepads work to move around the menu. Fortunately, I plugged in a USB keyboard into the nice new USB sockets that I added earlier and it worked fine the first time.
Now flash the BIOS as per these instructions. Once finished, assuming everything was successful, turn off your Xbox. Now with your new Cromwell BIOS still selected (bank 0) turn the Xbox back on. If all went well, you will be greated with the Cromwell BIOS screen that should show your new firmware version number.