To achieve 8-Channel Audio output, you have to connect the front panel audio module to the F_AUDIO connector on the motherboard. Then set the type of equipment from the audio software. The audio module should be the HD High Definition specification.
It is because Intel Rapid Storage Technology driver was not install properly in Windows Server operating system. Please enable .NET Framework 3.5.1 in Windows 2008 R2. You may follow the instruction below: