ok, so 800 watts of MH
and another 440 of VHO
... that's a lot of light for an 80 gallon tank!
if it's possible to trade off some lighting efficency for the sake of keeping cooler water, it might be advisable to build the light fixture in a contained box (wood box lined with insulation and sheetmetal, sealed with a pyrex glass window... lourved vents on the sides would let fresh air in
pyrex is known for it's ability not block UV
rays, and it takes heat real well.
with this sealed box, you can now install a dryer vent kit, and put a fan on the end of it, venting the hot air outside or someplace other than the tank area. this will keep conductive and convective heat from getting into your tank... radiant heat can't be helped, but the spectra of the bulb should be tuned to not generate too much infrared radiation.
advantage of external venting is you can have a mother of a fan on the end of the duct, and just put it somewhere that noise is not an issue (like through the wall into the garage or attic, etc.