After where your guide from matrix leaves off you need to use a program like jrunner or autogg to build a glitch image of your nand. If you are using rgh1 makesure its a rgh1 image if 2 then 2. If your using jrunner your image will be in a folder thats named by your consoles serial number. The file your looking for is named updflash.bin you will take that file and put it on the root of a usb drive thats formatted fat32 then put that in your xbox and boot xell with the eject button. xell will recognise the image and write it to nand and when its done will tell you to shut down your console. after that reboot and your on freeBOOT. (also a note to help building the image you will need your original nand dump and your consoles cpu key) cpu key is found on the xell screen when booted you will also want to keep your cpu key in a txt file with your original nand in a safe place.
Hope that helps