I would say that you would be better to go with more of them. I have them straight up the center and my tank is 84"L x 28"w x 26"D and as my corals grow large I imagine I will need to add a strip (maybe orphek) or t5 up the sides. In your situation I would say to look at 4 of them set diagonally which would cover the extra width and the length. An extra slave unit was about $235USD. They are also introducing the new X300 which is 36"long and more wattage. I don't know pricing.
As for my changes, I felt the original was a little too windex like. They now have a pre-made "super blue" option which has been popular and it mirrors the Radion G5 blue for look. I have attached what I did in this pic. In hindsight I think I would replace the reds with two Royal Blue as I get enough red in my low K whites.
