With a VDIMM voltmod on the NF7-S, and with an unmodified +3.3VDC rail, the highest VDIMM you will be able to get will be in the area of ~3.1V, likely a little bit less. To go above ~3.1V with a voltmod, one needs to overvolt their +3.3VDC rail. This is because the NF7-S feeds VDIMM off of the 3.3V rail.
Because of this, an OCZ DDR Booster is really the easiest, and safest way to get lots of VDIMM with this board.
I'm pretty sure that you can use a booster, and still keep dual channel with an NF7-S. You might need to bend one of the heatsinks, but I am quite certain that several people here have used a Booster successfully with their NF7-S, and two sticks of RAM in dual channel.