Reduce heat and also experiment with LEDs
Area-51 has a modular system which might fit your needs (for distributed light, not a monolithic fixture, although they can be connected to create one). 90w per light. That's not as tedious as my 18w lightbubs. You could use those on top, and your T5HO as sidelight. Use the 18w lightbulbs to fill in sidelight as necessary.
The A51 lights are spec'ed at 26w/sq ft. The Cree bulbs are around 35, although I find distributing light seems to create an efficiency and 30 seems reasonable. As mentioned before, your T5HO is supposed to be optimal at 40 (diminishing returns at past 50). So, you'd have to weigh percentages of each to figure out the w/sq ft you're targeting.
If you have DIY skills you could make your own COB lights, including low-power for close, distributed lighting (sidelighting too). I haven't made a COB but others could point you in the right direction.