Not to worry, RAM will work in Triple Channel mode. Page 16 (bottom section) of the manual states how you can install the four memory sticks to enable Triple Channel.
1. 3 Channel mode cannot be enabled if only one or two DDR3 memory modules are installed.
2. When enabling 3 Channel mode with three, four or six modules, it is recommended that memory of the
same capacity, brand, speed, and chips be used. When enabling 3 Channel mode with three memory
modules, be sure to install them in the DDR3_1, DDR3_3 and DDR3_5 sockets. When enabling 3 Channel
mode with four memory modules, be sure to install them in the DDR3_1, DDR3_2, DDR3_3 and DDR3_5 sockets.
From Back to Front (that's Slot 1 being the closest to the CPU socket), install as follows:
Slot: 1 Install
Slot: 2 Install
Slot: 3 Empty
Slot: 4 Install
Slot: 5 Empty
Slot: 6 Install
In other words, Install in all the THREE GREEN slots and ONE BLACK closest to the CPU Socket