Ok no problem.
Let say that u select DCT0 and set the timings 6-6-6-18, so, all ur RAM will run with that specs, u save that specs in the BIOS and reboot ur rig.
After that, u enter to the BIOS again and select DCT1 and set the timings 4-4-4-12 and do the same process that the 1st time.
In this part, we can see the DCTO and DCT1 like RAM profiles that u select it depends of ur needs.
Now, with "both" I mean that u enter to the BIOS and set the same timings specs for DCT0 and DCT1.