RE: Optiplex 7040 Enable AMT
I'm working on organizing my screenshots into an imgur album. I did this on three different Optiplex 7040's, so I'm confident it can be done. Keep in mind that you are modifying your system flash and doing this could render your system unbootable if there is an error. I'm not *recommending* that you do this, I'm just showing that it is possible.
Album (completely a mess) here: https://imgur.com/a/Mh9Jz
Essentially, you need to close a jumper on the motherboard marked "service mode." I used the PW reset jumper since I didn't have a spare laying around. You'll need to get a copy of Intel's Flash Image Tool kit - you're on your own, there - and using those tools, you can see the commands I ran to get the flash into a file, modify the AMT flag, and reflash the resulting file in the screenshots.