Extended vs. Standard is determined by your serial number.
If it doesn't say extended, then your serial number is for standard.
You can't force it because your serial number is not for Extended, and thus cannot use the Extended features.
Using the Adobe Download Manager we both chose to install the Trial version of Photoshop CS6 Extended and his worked fine, mine does not boot with Extended features. Why is this?
The trial version is always extended.
Any chance you're on XP (where no 3D or GPU features will work)?
Did you download the trial version of the software directly from Adobe.com?
What Chris is trying to say is that there's no known reason why the legitimate trial version from Adobe shouldn't enable the 3D features on a system that supports GPU operations, as you've said yours does:
My GPU is the ATI Radeon 6520G and it has support for both Open GL & Open CL. It appears in the Performance preferences with GPU checked and Open CL is selectable in advanced