I have never had a problem installing the AMD drivers for Windows 7 on Server 2008R2. But they are hard to find on AMD's site, aren't they.
What I have been doing is select AMD 9-Series Chipsets, and Windows 7 - 64 bit. This gives me http://support.amd.com/us/gpudownload/windows/Pages/raid_windows.aspx#2. Yes, it is the same sb driver as yours.
I just (re)installed the driver from the 12.8 package. It was at .\Packages\Drivers\SBDrv\hseries\AHCI\W764A in the expanded package. I am using Windows Server 2008 R2 SP1 on an Asus E35M1-M-Pro, with an E-350 CPU and the A50 Hudson M1 chipset.
Note, If your BIOS is like mine, it does not support RAID. There is no RAID option for the onchip SATA channel, only IDE and AHCI. So I have to resort to software, Disk Manager in Windows Server. I have a 2.7 TB RAID 5 on four, 1 TB SATA III drives. Each drive also has a 512 MB EFI partition and a 32 GB partition for a boot mirror.
Two: HD 4550, Phenom II x6 1090T on MSI 870A-G54, 16 GB DDR3 1333
Two: Asrock E350M1, 8 GB DDR3 1333
HD 5570, Athlon II X4 630 on Gigabyte GA-870A-UD3, 16 GB DDR3 1333
Dual HD 4650's in CrossfireX, on MSI RD 480 Neo2, 4GB DDR2 800.