I have never used the slayers' installers but from what I hear they have the contents of an xbox C partition on them. IF this is the case you could "hotswap" your way into the drive and copy the contents from the cd then lock it using xboxhdm using the Key that you wrote down. Again I have never needed to use the slayers autoinstaller so Im not really sure as to what they have on them (downloading one now to take a look).
Either way you are not hurting anything b/c 1.) you formated the HD!! 2.) you have an xenium (the best chip) on the way you can get your eprom from the xbox using the chip. So try a hotswap and if you just cant get it to work wait on the xenium, install it, then do a emprom backup 1st!! then restore your xbox HD. OH and a word to the wise dont use the format feature on xenium os as of version 2.0.1 its a little buggy i think. I have a tutorial on this site and mine showing the installation of an xenium (in my sig) good luck