I have the same motherboard Asus M2N68-LA (Narra3) with a phenom 9500 on it and wanted to upgrade the CPU to a Phenom 9950. Before installing the new processor I contacted the HP support and they told me the following:

"your PC is preinstalled with Phenom-9500 Agena 2.2 GHz (95W) processor.

The Maximum approved processor on your PC is:

Sempron less than 3800+
Athlon64 less than 4000+
Athlon64 X2 up to 5600+ (up to 89 watt TDP)
Phenom up to 9600 (up to 95 watt TDP)