i have done 5-6 duo x installs, none on a 1.6. you will have to find a specific bios for that. use the xecuter 2 bios made for the 1.6. you can use the cromwell bios to flash using a disk. its actually pretty simple. i think you want the euraisa flash disk, i think... search xbox-scene its an excellent site for xbox, also some tips off the top of my head are...

-you need a tool called xtool(something like that) its for editing the xecuter bios, you need to resize the bios from 256 to 512kb(again i think, its been awile so double check everythjing i say before you flash)

-right before it starts to write to flash, flip the dip switch on the chip, this will flash over your empty bank, and will leave the cromwell ok, just incase you have to reflash

uhhhh...i can't think of any thing else right now, i will be around all night tonite so if u need more help just let me know