Klipsch do tend to run their tweeters a bit hot, so they can be harsh to some people. Their advantage is they don't lose as much energy outside the flare of the horn's angle, which could be beneficial at a 18' listening distance. The Klipsch THX look to be voiced very neutrally though, however they are a bit more expensive than the Ascends. You would want to work a deal with those with a seller, there is room for bargaining on those. One aspect in your listening position that will serve as relief to the distance is it looks like you are seated against the wall. This would help boost the output of any speaker you get due to the first reflections behind you, but this may not be a good thing. you might want to place some kind of acoustic damping behind you. Anyway, the Ascends look to be terrific speakers, and if you are accustomed to lower listening levels, they might work fine for you.
One thing I just noticed is that you intend to mount the speakers close to the ceiling. I must have missed that before. This is going to cause a lot of havoc with the frequency response. I think this is an even greater argument for Klipsch or other horn loaded speakers as they will not be as susceptible to acoustic reflections as other flat baffle speakers. Here is one idea for you: the JBL 8320
s. They are made for those conditions. They are powerful, made for the ceiling/wall angle, easy to mount, and best of all, inexpensive. Plus, when you move and gain more ideal conditions for front stage speakers, you can simply move those speakers to the rear and use them as surround speakers, a role for which they are ideal. You can also kick it up a notch with that line and get the JBL 8340
, both are about $1k a pair. They will be quite a bit more powerful then the 8320 and have absolutely no problem tackling that listening distance. Any of these 83xx lines from JBL are THX certified, so they will be very neutral and have a very good response.