I can't really tell what size that tub is, it appears to be about 2'x 2' and about 3" or 4" inches deep - with all of your roots grown together into one rootmass.
If that's about right, you're too crowded and there's not much you can do about it! If you have all 11 plants squeezed into 4 sq.ft., that's only 1/2 the area a 400 watt HPS is meant to cover. And 3" or 4" of depth isn't near enough. Your roots have already grown into a solid mat. If you want to repot, individually, the only thing you can do is cut the soil "like a birthday cake" and hope for the best.
You are doing a SOG, whether it is intentional or not, is another question! Your undergrowth will be so crowded that you will "only" have a canopy - until you run out of depth and start to strangle. What I am telling you is a "Wost Case Scenario", of course!
What I would do, is cut the bottom off your container and "Double Stack" it onto a much deeper one, full of additional soil. Then start some "Serious" LST (Low Stress Training), to try and spread those "Puppies" out to a full 8 or 9 sq. ft. canopy. Good luck!