I am running into the exact same problem.. I have tried 2 programmers and several loaders. The Chip is not detected. What I did try was X2cable, which is DOS based. What I found there was that I still could not flash the bios, but I could read it and save a copy of it.
Any help with this is appreciated, and just so you know, I haven't bothered putting this in the Xbox because I figured if I can't load the new Bios, then it is not doing me any good, so I have no idea whether the box will boot with the chip in place.