Okay, I figured it out...

For anyone else that may have flash drive problems, even though my drive was already factory formatted FAT32, and even though I never had a problem on any computer with the drive, it threw read errors in the head unit. I re-formatted again, and it works great. There may have been some root files I wasn't seeing (ur3 flash protocols maybe...) but all the excitement is over.

Now I can obsess about something else!