If you can make equal lengths for each light, that seems like it would work out fine. If not, some will pull more air than others but at 40f, it won't matter much :) The air will take the path of least resistance.
I have 3 of those ice boxes and tested them out for a few hours. In my case, it sucked all the humidity out which I needed since it was a veg room. It does blow cold air but it makes your chiller work pretty hard. And lots of heat from the chiller so that has to be in another room. You need a HUGE chiller or it's not very effective. It's supposed to be more efficient than A/C but there are more things that can go wrong. Fan, chiller, water pump, leaks, condensation on the lines...and so on. Great idea though and i'll do another test on it at some point.
I even thought about just having one of my cool tubes with the icebox. In a 5 light setup, I could icebox the middle light and add a little cold air at the same time. The other 4 lights will remain as is with the ducting. Lots of possibilities! Gives me a headache sometimes lol!