Hi there,
I have found that it is actually better to manually set the speed, timings and voltage for RAM rather than using the profile settings.
By default the motherboard will have set the RAM to the JDEC Standard of 1333MHz at 1.5V. Depending on which models of Dominator RAM you have you may find that to go above 1333MHz you will also need to increase the RAM Voltage to 1.65V.
The Speed and Timings of the RAM are set in the MIT Section of BIOS under the sub-heading DRAM Configuration. Change Set Memory clock to Manual then the Memory Clock option becomes available and you need to change this to X8.00 (=1600MHz).
DCT's Mode should be left at Unganged
DDR3 Timing Items changed to Manual then the Timing Options will become available. Here is where you change the timings for your particular RAM Modules. You will need to check these against their specifications but will be something like 9,9,9,24,2T
To change the Voltage for the RAM (if needed) you need to change the System Voltage Control in the MIT Section from Auto to Manual. Then change the DRAM Voltage to the rated value for your RAM.
If you are running an Athlon or Phenom ii processor on the board you might want to check this thread before changing anything:
http://forum.giga-byte.co.uk/index.php/topic,2515.0.html