OK....I went to my LFS where I bought my Emperor 400 two months ago and asked the owner about the filter. The new Emperor 400 does not have the flow control knob. Yes, the 400 has the intake extender for deeper tanks and an adjustable mid-tank intake but that is not the flow control. The owner of the LFS even went as far as to show me the manufacture date on the Emperor 400's he had on the shelve and they'd all been made within the last month or so. Since I bought pretty much my whole tank set-up from him (tank, stand, filters, gravel, test kit, etc) he's kind of in to keeping me happy and wanted to make sure I wasn't thinking he sold me "old" stuff. I didn't let on that I'd kind of like the older model with the flow control.
Might add that I took the intake extender and put it on my 280 which is on a 37 gallon tall show tank...works great. The 400 pulls from mid level and I run a fluidized bed filter at the other end of the tank that pulls from just above the gravel.