Mitch4t, yes you should be able to dial down/EQ the bass from full range speakers, which should work ok for your sidewall seating arrangements you presently have. Perceived bass will still be strong near sidewalls where you sit, but weaker in center of room overall, and anywhere out from sidewalls/corners. This will help your diliema if neighbors are a problem with your room construction acoutical issues.
Also, your horn speakers you're considering should help immensely with your sidewall speaker and seating locations, since you have so much sidewall reflection and slap echo issues right now. Would also help to toe em en a few degrees. Yes, horns are your best friend here, and HIGHLY EFFICIENT DESIGNS FOR ADDED DYNAMICS ..all things equal. So, yes, I like horns for you. also Klipsch's are worth a consider as alternative if CV's don't work out for your liking for strictly HT dubties.
Another strong consideration to smooth out bass and get proper perspective and added pressense from the speaker system is to mount your front L/R speakers and rears up the walls! I'd like to see you get those speakers off the flooor for acoustics and as big as your screen is, will match better and offer for pressence and grandure to the sound, IMO - just like commericial cinemas. In fact, more you duplicate their setup's, closer you are likely to your goals.
Another thing, I've seen your setup for years. Don't know how you live with slap echo and first order reflection issue with present setup, and seeing a double image from screen in that huge right wall mirror!...YEIKES!!!
Have you considered a "long wall" setup for your HT system?
You could easily free up more space, and yet still have a massive screen and potent setup flipping your system "sideways" - and going with smaller but still very large and wide 2.4:1 widescreen setup. Whether you put the screen opposing mirror, or where mirror is now, either way will make the visual experience much better than it is now, and take the reflection you see out of equation! I'd probably lean toward putting screen opposing the mirror, however.
Acoustical performance from your seating positions would also be WWWWWWWWWWAAAAAAAY BETTER doing a long wall setup as well, cause no sidewall reflection problems to deal with, and a much more spacious sound, where you are heaing much much more of the direct sound from the main speakers, instead of simultaneous delayed reflections off sidewalls! It's a consideration I'd strongly choose for you, if you can't treat mirror and sidewall refletions. This is fact. Never the less, if you can't, yes horn speakers are likely best options for you, for what you're after. Also, ACTIVE horn speakers will be even more dynamic and powerful (e.g., what IMAX uses)
If you do go "long wall setup" at some point, and you would consider that option, it will also have added benefit of letting you free up much of the space for much needed decor, furnishing, and decoration considerations on the ends of the room! I simply think there's lot left on the table here for all aspects of the room, even if you never do acoustical treatments in the space.
Hope this helps.