Yeah, so while in the process of reading as much of the forum and the 8094864 pages of info within, I neglected to notice that some models use different software image files of windows CE.
So while I booted my 500bt into CE, cleared the My Flash Disk folder, and loaded everything into it correctly... there's no way it will run without that correct image file.
I read in the FX3.1 thread that someone had used a 500bt image and got it to (mostly) work, but where can I find this? I have no Pioneer firmware SD cards from which to grab an image file.