You'll be fine running the T5s alone. Also, for $600, you could possibly find a better LED supplementation rig than the ATI LEDs. Depending on how your lights are hung, you could possibly add a couple of Kessils to supplement color and spot intensity. I ran a Kessil/T5 combo in the past and it looked great.
That said, I switched from a 24 inch, 6 bulb ATI fixture for a Radion XR15 over my 60 cube a few months back. I'm very happy with the change. Almost all of the disco ball effect is gone with their new LED arrangement. You have to look for it to see it, and it's still pretty subtile. The software allows you to tune the color to whatever spectrum you want. It's really easy to keep it from getting too blue while still getting good florescence. They're not cheap lights, but you won't have to replace bulbs again.
If you decided to go this route, give the BRS videos a watch. They have some good recommendations for when you should buy the XR30 vs the XR15 for a given tank length.
You could also work in a DIY rig. My ATI light had a single row of LEDs screwed to each side. The guy that made it just used a heatsink that was about an inch wide. He mounted the chips to it without lenses and the spread was great for adding color to the tank.