I have my IMG graphite cone version of the Kappa6 working now. I've opened the back of the midrange chamber, and let me tell you why. This is going to be bit if a ramble, so be forewarned.
I wandered into a high end store here in Atlanta the other day and auditioned a pair of gorgeous 30 thousand dollar Sonus Faber Amati Tradition speakers. They are basically the updated version of a speaker I used to own and love, the Cremona, with a very similar cabinet design and Scan Speak driver compliment but with one huge difference which neither the salesman nor Sonus Faber seem to want to talk about; the back of the speaker is open! It's like an open baffle speaker with the baffle wings folded back on themselves until they almost sides almost touch, leaving a two inch wide slot that runs the entire length of the speaker (see photo). If you peer inside, you'll see the backs of all four drivers in all their glory, just like in an tube old console. The mid is no longer in a separate isolation chamber because it doesn't have to be, the open back removes the pressure from the woofers. I'm sure they've made improvements in the drivers and crossover in the past 15 years, but these were simply orders of magnitude better sounding than my old Cremonas, especially in the midrange and bass. In my mind this is the most ingenious speaker cabinet design in decades, maybe ever. The woofers don't experience cancellation like in a true open baffle so the slot loaded low bass is superb, and I do mean superb, I was astounded at the extension and clarity (I have JBL 2245's in an infinite baffle), and you get all, or at least most of the benefits of an open baffle design, but with a narrower, and in my opinion better presentation.
A pair of Kappa6 popped up locally at a good price so I decided to do a quick test of the benefits of open back midrange. I had an extra pair of the IMG mids Infinity used in several models including the very nice sounding Crescendo, so I popped them in and routed out the back of the midrange tube. After a quick crossover tweak I tested an open versus closed tube version and the difference was, dare I say, (you guessed it!) night and day. In addition to removing the backwave reflection and all the other garbage that builds up inside the tube, you are lowering the fundamental tube resonance from 700, just bellow the 800 Hz crossover point, to 350 where it no longer gets excited. I really wish I had a pair of EMIMs on hand to see how they would sound in this configuration, as that tube noise bugged the hell out of me in the end.
Do they sound like $30,000 Sonus Fabers? Of course not. But they do sound great. The low bass is the biggest problem now, with lots of box noise and distortion, so rolling them off at around 60 Hz so into a sub would help a lot. Just a note; the previous owner is responsible for that woofer refoam job.