Its still pretty easy and you don't need a programmer. 1st install the chip on the 1.6 Xbox and set it to Bank 1 and boot the Xbox to evox, once its booted move the switch to Bank 0 and flash the chip. You should now have 2 banks with a 1.6 Bios.
For xboxes 1.0-1.5 its the same thing. 1st install the chip on the 1.0-1.5 Xbox and set it to Bank 0 this time and boot the Xbox to evox, once its booted move the switch to Bank 1 and flash the chip with a 1.0-1.5 bios. You should now have 2 banks with a 1.0-1.5 Bios.
As far as the Xecuter programmer, I beleive it doesn't work for the Duo's (not 100% sure)