W00TZ!!! Turns out the MBB and PSU are both actually fine! I just had one of the PCI-E rail floppy connectors plugged in wrong , and apparently both the PSU and MBB are smart enough to not power on in such an event.
EDIT:
...and down again....
As it turns out, the MBB was not happy with the PSU that I had modified for the case. Apparently it wasn't providing enough current on the 5V line, though it supposedly only needs 2A and the PSU is rated at 2.5A. As a result, it would power on, but do nothing and show nothing on the post code LEDs (which is what tipped me off to try a PSU with a higher 5V current rating). So I hooked up my 700W Thermaltake Toughpower, which is rated at 3A on the 5V line.....now it powers on but does nothing but spout gibberish in the POST code LEDs. I tried clearing the BIOS, and now it just spouts different gibberish.... ...this is really putting me off DFI....
EDIT:
So, as it turns out, DFI's support is quick...but very unhelpful.
Only about 30 minutes after I sent in the ticket, I get a response: "I would rma the board with the your place of purchase."
...gee thanks, I'm so glad that didn't cross my mind....OH WAIT. (Unfortunately, NewEgg put a 30-day limit on replacing the board, and it's been 35 days...I think I'm gonna try contacting NewEgg, see if they'll make an exception.
EDIT:
So, at least he gave me the email address for the DFI RMA dept (something I could not find on their website). So I guess that's what I'll be doing....now to extract the MBB from this case...