OK, first up sorry my suggestion caused you so much trouble. As you said, I've never had trouble flashing a drive before, though it's one of those things that's always in the back of your mind as a potential problem. The good news is, if you have a floppy drive it's relatively easy and if you don't it's still possible with a second optical drive connected.
Here's what you do:
Download mkflash 1.80:
Download this boot-floppy creator:
Now, if you have a floppy drive get a blank and use the floppy creator to make it boot DOS. Unarchive and the MTK180 files to the prepared floppy as well as the backup of your original firmware you made before flashing (something.bin) -- make sure to shorten it to something easy, DOS doesn't like long file names. Shut down.
Set the drive as slave and put it on your secondary IDE channel, alone, but disconnect the power from it. Leave the side off of your case.
Boot from the floppy you created and type DIR, taking note of the name of your firmware, something.bin. Reconnect power to the DDU1615 -- yes, I know this is generally stupid, but here it's the only way to get the machine to boot, and the drive is already "dead", so do it anyway. Once the drive is plugged back in type:
MTKFLASH 4 W /B /M something.bin
Breakdown of the options used:
4 tells the program it's the slave drive on the secondary IDE channel
W tells it to write
/B tells it the image is in binary format
/M tells it the image is multibank, read from one file
something.bin should obviously be changed to whatever you called the file on the floppy.
Press enter, wait for the flash to finish, and reboot. The drive should again be recognized as a Sony DDU1615.
If you're still feeling adventurous (I doubt it, but here it is anyway) you can get rid of your rip-lock by modding the backup .bin you just flashed with OmniPatcher and reflashing the drive (with MKflash this time, as it is apparently safer/more stable, though I've never had trouble with the Windows app...) to unlock it.
BUT WAIT, I DON'T HAVE A FLOPPY DRIVE!
In this case you have 2 options.
The first is to steal one from somewhere for the purposes of this little project.
The second is to make a bootable DOS ISO with a writer and include MKFLASH and the firmware backup.bin.
If you can't get a floppy drive tell me, and I'll work out just how to make this ISO. Otherwise, best of luck.