I've never done it, but I believe you can go 6 deep, not that I ever would. I am two deep at this time for one miner in one room just because I haven't pulled it out yet.
I added another switch and now can run the Avalon6 and S5 together for 4.7TH. Good thing it's been cool the last few days, I haven't needed to use my heater at all.
Nice Pic
Another Pic Come On