Old Am2+ CPU question.

Solution
The Phenom II x 4's (AM3 Socket) are included in the mobo's Supported CPU's list, so they should work... it may require a BIOS update though, but any of the AM3 CPUs included in the support list, should have no issues working. You can find BIOS download links in the motherboard page Support link, or you can install the "MSI Live Update 5" tool to help find and download the right BIOS uipdate.

MSI K9A2
http://www.msi.com/product/mb/K9A2_Platinum.html#hero-overview

Supported CPUs List
http://www.msi.com/support/mb/K9A2_Platinum.html#support-cpu
The Phenom II x 4's (AM3 Socket) are included in the mobo's Supported CPU's list, so they should work... it may require a BIOS update though, but any of the AM3 CPUs included in the support list, should have no issues working. You can find BIOS download links in the motherboard page Support link, or you can install the "MSI Live Update 5" tool to help find and download the right BIOS uipdate.

MSI K9A2
http://www.msi.com/product/mb/K9A2_Platinum.html#hero-overview

Supported CPUs List
http://www.msi.com/support/mb/K9A2_Platinum.html#support-cpu
 
Solution