You want to use the bulb heat for the leaves what led guys are at with the vpd or whatever .. then you can keep the room cooler to
Like sitting round the campfire type thing
I used air cooled hoods for over 10 years. There is no lack of heat or specifically IR for the leaves to stay warm. The hoods remove the excess, its not like they air condition the room to a lower temp. In the winter when I did need extra warmth, I just unhooked the ducting and let the air circulate in the room. It still removed the hot spot directly under the light, and allowed me to run the light closer to the canopy.
Some people complain about the small amount of light that diffuses through the glass but that really isn't an issue either. With less heat intensity directly over the canopy you can lower the lights closer to the plants without any issues which then directly increases the amount of light they are getting, so no real loss.
While I do agree that using 8 600s in an 8x8 space would a lot it wouldn't be totally crazy, many people have used 2 600s in a 4x4, at least back in the day. It gave better coverage then a single 1k, and only used a little more wattage.
Really I think the answer to this would be 6 lights, 3 down each side like I mentioned in my first post. That would provide you with excellent canopy coverage, and still about 50 w/sqft to ensure plenty of photons for good strong growth.