Knowing HP, they probably want that Mobo in their own case. However, a test on another case should work (cant see why not).
You could also try (and I dont know if they would have this) to update the mobo's BIOS. They might have revised it and added / enabled an option to turn those notifications off.
Also, check the HP support site for our original HP Model No, they might have some more info on there about the problem (its not wholly unheard of that the front USB / Audio could burn out or die, so its silly to build that in and not be able to turn it off.
Just a few ideas