Until I poked around in Nero.
I tried to create this one the same way I did the DVD-5 - unpack the ISO with WinRAR to the hard drive, then use "Burn DVD Video files" in Nero to burn the disc. I tried selecting the ISO file in that process, but Nero wouldn't recognize it.
Tonight, I poked around in Nero and found "Burn Image to disc". THAT recognized the ISO file. I burned that to a disc thru that option in Nero - without the Imgburn fix applied - and the disc works flawlessly!
Sorry for all the confusion.