tri channel vs dual channel

Ok so I am about to build a new amd comp and wanted to go with 8gb of memory. My question would be whether or not I would be able to buy two 2x3gb kits and sell a couple of the sticks and just use the other four. Would they work the same or is there something inherently different between tri channel kits and dual channel kits?

DDR3 triple channel will run in dual channel if there are only 2 modules, so I am sure it will run in dual mode if there are only 4 modules.

the only thing different is the voltage used for those speeds/timings....

Why not just buy a dual channel set of ddr3? It will cost the same after you sell the old sticks, but this way it ELIMINATES any issues with compatability.