Your board only supports cpu's with a 95W TDP.
Amd makes 95W and 125W+ versions of the same cpu in some models.
The cpu you linked should be fine imo it's a 95W version.
Some versions listed in the support lists may have different model # = oem tray versions or earlier retail versions.
As always, Davcon. Thanks for your experience, and time.
I'll pick up the 840 next week. Maybe I'll get lucky and it will unlock successfully.