Ram is a bit of a sensitive creature. Since they are both PC3-1600 they should work together (as long as both are ECC). In the BIOS if you can set ram timings, you will need to set the timings listed on the slowest module. This means highest numbers. (higher means slower)
Only resort to manual timings if you are having issues with BSOD's or lock ups. The Motherboard and BIOS should auto detect the slowest module, but that's not always the case.
Hope the helps a bit.