Welcome to the forum, Brian. You've got some pretty serious speakers there. The KLFs are the last of the "manly" speakers from Klipsch before gearing towards smaller HT models. Isn't that center channel 40 lbs or something?
I used to own a pair of KLF-20s. They doubled as two channel and HT speakers. Used another (smaller) center channel because I couldn't fit that giant C7 anywhere. What I liked about the KLF-20s was there power and dynamic range. They made for really fun HT front channels. The one thing I didn't like about them was the listening fatigue. I know, that term is bandied about anytime someone mentions Klipsch, but my ears didn't agree with the horns after extended listening. Other people have no problem with fatigue, so it really is a personal preference. I just don't want you to think I'm knocking them based solely on popular opinion. I have a soft spot for Klipsch because they were my first set of serious speakers.
Unfortunately, I don't have a lot of experience with comparable Axiom products. I own the Axiom M40s, a discontinued tower that plays more on the mellow side of the Axiom sound. While the KLF series is pretty "in-your-face" in terms of presentation, the M40s are a lot more polite. That being said, I can only recommend on information I have gathered from other members here. So. . .
Since the KLF-30s are big full-range speakers, I would say to first look at the Axiom M80s. These will give you just about the same frequency response in a smaller cabinet--shorter and slimmer. What you may be giving up is some visceral impact. The M80s two 6.5" woofers will not move as much air as the two 10" drivers on the Klipsch. You will probably gain a bit more refinement on the bottom end, though. And if you use a sub it will help with the impact.
As far as the overall sound, the M80s will probably be close in terms of presentation--meaning up-front and detailed. You may have to play with set up a bit more to find the sweet spot. Those horns throw out a pretty wide soundfield.
I don't know what you intend to use for rears, but if you want to keep the same speakers all the way around amplification will be an issue. While the Klipsch are an easy load (8 ohms, 102dB sensitivity) the M80s (4 ohms) demand more out an amp. It will be a fairly significant load if you are listening at loud levels.
Another option for the surrounds is to go for the QS8s. Again, I have no personal experience with these, but you will be hard pressed to find a better surround speaker if you are looking for enveloping sound. These will not be close in terms of frequency response, but if your main viewing is HT there is not a whole lot of full range surround signals being sent to the rear. If you like multichannel music, that is another matter. A bonus for the QS8s is the size. These can be wall mounted and will be a big change from floorstanding rears.
Overall, I'd say the Klipsch offer a big powerful sound. With the Axioms, you may lose some overall impact (again, a well-integrated sub can atone for this), but you will probably gain in terms of refinement. Given the proper amplification, the M80s are very capable of lettin' loose without loosing control.
Going from horn speakers to traditional dome tweeters is a something of an adjustment. You may need to audition them side by side and give your ears a chance to familiarize themselves to the different sound.
I don't think many others here have had experience with Klipsch speakers. Sorry I don't have direct experience with the comparable Axiom speaks to give you any concrete information.
Good luck, though. And you might want to see if you can set up an audition if you have any local Axiom owners near you.
