Costin,
you can do it by serial guide at the beginning of the guide to be certain. 'Kindle DX Graphite: Serial no. prefix B009'
easier just look at the bin files. as long as you know the real name dxi vs. dx vs dxg the files are labeled.
also you should note on some versions the U006 is supposed to happen. "On FW 2.x only, the jailbreak update process will FAIL (with a U006 error in the lower left corner of the screen) but that's okay, it's supposed to.
"
so assuming we are doing newest version jailbreak from this wiki and newer kindle, then you should get two successful updates, one with jailbreak and one with ss before dead people leave.
also i found you must do them in this order to work- jailbreak then ss hack- but it didnt hurt anything to have done the ss first by accident (failed of course).
for mine, it has only wifi and is k3, i used the "k3w" bins. but i didnt try them till i also checked the serial. i dont know if doing other wrong jailbreaks will affect things, wouldnt hurt to unistall them and dont forget to reboot after each update.