Little more info, after I'm skimming through the manual for his board. In the M.I.T - Advanced Memory Settings there is an option for "Channel A Memory Sub Timings" and Channel B Memory Sub Timings". I believe that's what he was referring to. It seems the frequency has to be the same between both channels, but you can set different sub timings (CAS, tRCD, tRP, tRAS, etc) for each channel. Not sure what the benefit of this is, and/or if it's recommended to run each channel on different sub timings.
Main: i5-3570K, ASRock Z77 Pro4-M, MSI RX480 8G, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod