Thunderbolt Firmware Update 1.2 won't install on Late 2012 Mac mini

I have a Late 2012 Mac mini 2.5 i5 with 16GB RAM and a Crucial M500 960GB SATA SSD running OS X El Capitan 10.11.4.

Since mid-November 2015, I have made several unsuccessful attempts to install Thunderbolt Firmware Update 1.2. I have followed Apple's support recommendations (example: Thunderbolt Firmware Update 1.2: Keeps reappearing and Thunderbolt ports and Target Display Mode may not work - Apple Su… ), I have tried resetting the SMC controller, I have tried booting into Safe Mode, I have tried completely formatting the Mac and reinstalling a fresh copy of El Capitan, and I have even tried begging. Nothing works. After an installation attempt, I get a number of error messages before OS X fully loads, then the computer restarts itself again, then I return to the login screen as usual. Below is an example of one of the errors. I have also attached a photo of my screen.

[ASSERT] error: 14 (0x800000000000000E, Not Found),err == 0 ,

[ASSERT] where: ? ./Platform/Apple/Common/Library/DrawingUtilitiesLib/DUImage.c",

line: 565, "DUImageLoadFileFromFV"

Please note that I do not have -- nor have I ever had -- anything plugged into the Thunderbolt port. My monitor runs directly off the HDMI port. Note also that I've even made sure I don't have any USB stuff plugged in during installation attempts.

This issue started AFTER I installed the SSD into the Mac mini. I used Super Duper to clone my original drive, then I migrated everything to the SSD. Everything worked fine except this update. I'm wondering if I physically damaged the Thunderbolt port during the upgrade progress, although I'm almost certain I didn't. I'm an Apple-trained former Genius (direct -- was never an FRS) (I was also an Expert in the Red Zone) and I still can't figure it out. One problem is that I no longer have access to any of Apple's internal support resources.

At this point, I'm thinking I should just move on from the Mac mini. I hid the update and ignored it until recently when I tried to use a second monitor with an active DVI to Mini DP adapter that works perfectly on the 2015 15" Retina MacBook Pro that I use for work. When I plug it into my Mac mini, however, ALL my i/o crashes (including USB). When I unplug it, all my i/o works again. No restart necessary.

At this point, a trip to the Genius Bar is warranted, though I'll have to restore my original components (RAM, 5400 RPM HD) for them to even consider it for service. However, this defeats the purpose of the SSD, which freaking screams. If everything works fine with the 5400 and I go to reinstall the SSD and the same problem happens, it does me know good other than isolating the fact that the issue does indeed involve the latter.

If anyone has any unique suggestions that aren't in any of the existing Support Community posts, I'd really appreciate it. I've been pouring through this stuff for a long time to no avail and it's clear it's a wider issue than not found on multiple Mac iterations irrespective of SSD usage.