I somehow get the feeling you did something wrong using the KF940. Incorrect or missing time alignment or maybe non suitable crossover setting to the tops come to mind. Properly set up they hit much much harder than any vented direct radiating double-18 ever could, especially in the 60-80Hz range.
Outside...yeh...they do. All my posting was about indoor use. Outdoors you do get punch! Indoors..well...just sharing my experience. Remember that a horn load sub radiates differently in the near field. Have you tried 2 or 4 KF940's in a smaller/medium sized room before? I remember a church that wasn't very deep...maybe 60'? It was wide...maybe 100'? It's been a long time ago, so I don't remember much! Anyways, I think we had 2 KF940's a side, with probably 1600 watts a box. I vagely remember getting sick from the low frequency, but the punch just didn't seem to be there. Now, we used 6 or 8 KF940's a side on our big shows...8, 10, 15 thousand people. Sounded pretty great for that application. We've used BSS, XTA, and Lake for our processing and I'm a bit familiar with crossovers, timing and phase issues and I took quite a bit of time with Smaart doing system tuning (phase, xover, eq, etc). But...that was the big shows...for all I know we might have just set and plugged in those smaller shows....so you might be right that we were not running optimium settings.
Keep in mind these generated a LOT of moving air! Indoors I was looking for a certain type of sound (punch) and I just didn't like what I heard. I say give them a try, couldn't hurt! Maybe you would like the sound. I did like the sound outdoors, it was just in smaller rooms that I didn't really "feel" the kick drum. If you played a 20hz note on the keys, you would get dizzy the output was so precise and enormous. But hitting the kick? Nope...didn't ever sound good to me. I've had just a pair of double 18's in small rooms that I thought sounded much better. Overall possible output below say 80hz...oh the 940's win by a big margin. Just the "type" of moving air didn't quite set right with me at kick fundamental frequencies? It's really hard to describe....
We eventually got rid of a truckfull of them and switched to JBL double 18"s. Honestly, I liked the punch better with those...but I really missed the low stuff...like tracks or keys through the KF940s. No matter how many 940 boxes we had outdoors...always sounded very "hi fi" to me! Plus, they didn't have that cone distortion (especially around kick frequencies) that many 18"'s did...drove me nuts when we switched but I eventually got used to it.
Anyways, we did several indoor shows with the 940's and I just never got the punch I was looking for. Tried all kinds of stuff. If you look through the PSW posts from years ago, you can find details on the stuff I tried and checked. Keep in mind none of the indoor shows were very big. For outdoors, as I recall, when stacked in blocks of 4...it seemed like it took some distance for those KF940's to really punch. You could stand in front of a block and it wouldn't blow out your ears...but you could feel the kick drum like 4 miles away!
Really amazing output for 12" 800w speakers in a 13 foot horn....quite efficient they were....but at 400lbs and refrigerator sized...well, just say I had my fill of stacking them! I say give em a try! I'm a big believer in experimentation...if you like em..great! If not...on to the next!
PS: If you put 4 of these in a small room and play EDM...the cops *will* be there! Don't ask me how I know! ;-)