Cabighed,
I mentioned that there will be a grow journal posted very soon for this unit. As far as adding two 600w's, that's totally possible but up to the grower. The idea for this system was based off of Heath's unit. We added a few other things to the mix including aero and a ballast. His unit came out to be about $1000 USD. Ours can't be made by us for less than $1000 USD at the moment, and that doesn't include labor. But, I'm guessing that if Heath was going to market his product it would go for somewhere around 2000 if he charged for his labor costs. So with a recent grow this has yielded well using almost the exact same situation as Heath. If the unit isn't impressive enough the way it is then there will inevitably be modifications.

Since the tentative price doesn't seem to be sitting well for most of the DIY crowd, I would suggest sourcing the parts, adding up the man hours, and doing a cost analysis to see if this could realistically can be had for much cheaper. If so, and you're interested, build a vertical unit.