Horn Speakers and Sub Woofers

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.

I have never had K-horns. Always been a big Klipsch fan though. I set up a home theater system with Cornwals as the front mains, Heresy for center, Forte's for the surrounds and some cheap plastic Klipsch for the rears. I used a Def Tech 15" powered sub and it was the best home theater system I have ever heard. Period. 

Moved twice since then, all I have left are the 1989 vintage Forte's. Good luck, nothing does movies like super efficient horn loaded speakers.