The GTX6500P card is feature code 2843 or a type 1-Z card.
The 9124 adapter placement guide does not mention this feature code so I guess it is not supported by the system:
http://publib.boulder.ibm.com/infoce...xplacement.htm
From the list it looks like the system / firmware only supports the GTX135P - feature code 2849 - graphics card..