Hi there,
Enabling Dual Channel is done automatically, just so long as you insert your Memory modules into the appropriate slots on the motherboard (check User's manual for correct configuration.) As you are going to be populating all four slots with RAM you don't need to worry about this.
Depending on how you have configured the BIOS the only indication that I am aware of that Dual Channel mode is enabled is during the POST stage of start-up when it shows the initial POST Screen with memory, motherboard, CPU details.
Once you are running Windows you can use software to confirm Dual Channel memory configuration and the one that I prefer is CPUZ which you can download from here:
http://www.cpuid.com/softwares/cpu-z.html Once installed click on the Memory tab for details of your RAM.