Horn Speakers and Sub Woofers

To the general question (horns with subs) rather than the specific K-horn scenario, you could check out Avantgarde speakers which use that approach. I've heard them many times and have never noticed a problem with low end integration.

FWIW

There's nothing to be concerned about with HT, all you have is processed fake sound effects. 
david

["There's nothing to be concerned about with HT, all you have is processed fake sound effects.
david"]

Not to be a smart ass but they now have these things called music videos and the ones on BluRay can have rather good audio. I also enjoy the few multichannel SACDs I own on the HT.  

Not to be a smart ass but they now have these things called music videos and the ones on BluRay can have rather good audio. I also enjoy the few multichannel SACDs I own on the HT.

OP's question was specific to home theater & movies!
david

A horn stops acting like a horn where the size of the mouth of the horn is 1/4 wavelength.  That's why the Klipschorn is in the room corner.  It uses your room corner as part of the horn.  What I don't know is given the flare rate of an exponential curve, just how big a mouth that effectively is. 

One of the other posters here suggested the 7 foot Klipsch theatre sub-woofer.  A 7 foot wide mouth is a quarter wavelength for a 35 hz tone, so it only acts as a horn down to 35 hz.

I suggest you just be happy with your K-horns as is and forget the subs.