i have seen a ton of cooltubes all inline from one fan...especially if you use the tubes that house 2 lights in one however they are not nessasary, personally i would use the 7 600's i used to run 4 1k lights in a bedroom and it worked but have since changed over to 600's i find that while 1000's put down some fire you get much better coverage with 600's and more ight actually reaching the plants because they can be much closer.....which will be huge in your setup using cooltubes.....while they run cool and all that they are actually a shitty reflector compared to standard hoods when it comes to the footprint they put down, i would suggest this, if your hell bent on cooltubes then 600's will be by far your best producers, now if you want 1000's then i would suggest some different hoods like hydrofarm radiant 6 ac's or for a wider footprint their daystars 8 ac are a killer choice i use the radiant ac's and i use a single 100 cfm fan to cool them, check my vid on youtube called "stanky tent" and you will see what im talking about......oh but about your question you could cool all the 600's with a well designed duct system say like a single 10 inch maybe 500 cfm fan pulling through a splitter/reducer to 2 rows of lights like say 3 cooltubes in each row running the length of the grow space with a single fan pulling on the splitter so that it has in effect 2 intakes