Furman PL-Plus C is a relatively deep unit, and it gets warm by itself (all the power units do). I experimented various arrangement in my rack, including Furman 8X2 power unit, another Firewire interface, preamps, headphone distributor, etc, but only acceptable arrangement was the unit above UFX is very short, or non-heating unit like XLR patch bay. Otherwise, it got pretty warm. RME assured UFX's heat is not a problem, and I've never experienced instability or any problems with these units on top of UFX and pretty 'hot' UFX. So, I'm probably too much paranoid, but when I touch the front panel of UFX and touch the UFX's top panel when I removed the unit above, you'd understand what I mean. I just decided I give a blank space above UFX, with a mesh blank plate, then I have zero concern now.