Domes and CDs sound different, and domes tend to be less efficient, so will struggle to get the sound to the audience in comparison, especially over longer distances (the square rule applies for distance). If you need to turn the volume up more you've more chance of distortion. Domes (unless in a waveguide and there are some) tend to spray the sound in all directions, whereas CDs with waveguides aim them more at the audience and less towards the walls floor and ceiling, so better directivity and less treatment needed for reflections. Domes can be said to be a little warmer and less detailed than CDs, but I would think in a direct comparison you'd still hear all the same sounds, just with a difference. Perhaps the CDs sounds as if they have more 'clarity' but those kinds of descriptions like many in the audio world don't really tell you much technically. It may just boil down to personal preference. Waveguides can potentially have issues with the sound bouncing around within the waveguide before exit so if that's audible that's probably not a good thing. Pros and cons with both designs.
I can't really explain why I prefer CDs, but I do, and I think it's the type of sound which tends to sound a bit more visceral than the domes I've heard. I tried some PA speakers, many of which didn't sound that good, but I did find some that sounded fine (to me at least) and measured well, and I ended up with some Behringer B215XLs (tried one, liked it and bought two more). The crossover could do with tweaking to bring the crossover lower, but having heard some other more expensive and highly rated CD design speakers, I'm not sure that the extra cost is warranted for me. Definitely a case of diminishing returns. Here's a link to an AVS thread pertaining to the Behringers:
www.avsforum.com
For the price of one, for me it was a no brainer to buy to try and test. If I sold it on I wouldn't lose much and that loss is just the cost of getting some experience which can often be priceless.
With speakers there's definitely a thing that more expensive is better, but from my perspective that might be the case, but the amount of better certainly isn't always reflected in the price difference. Having said that, the best speakers I've ever heard are some ATC SCM300s, and they use domes, not CDs with waveguides. At around £45k new, they should be good:
atc.audio
Other speakers that get rave reviews that use CDs are the JBL M2s (much more affordable):
M2 Master Reference Monitor Addressing the growing need for high dynamic range and reference-mon...
jblpro.com
I did build some 8" speakers using a design found over on Audiokarma and other places that was started by a guy called Zilch (RIP. See link below for the details), and that cost a little more than the Behringer's. It uses a Constant Directivity waveguide (a highly recommended design for it's off axis delivery and good sound power reproduction) and works well. I'm not much of an audiophile (so take everything I say with a pinch of salt), but others have said they image well (when they listened to mine), so work well for stereo/music listening too.
******** Project Summary: http://audiokarma.org/forums/showthread.php?p=1856214#post1856214 Member Projects and Acknowledgments: http://audiokarma.org/forums/showthread.php?p=2260584#post2260584 Member Listening Impressions...
audiokarma.org
Google Econowave for more of the 'movement'.
DIYSoundGroup grew from Zilch's idea, and the SEOS guides are their waveguide design. This is their home theatre page, but plenty more designs there:
Speaker kits used for dedicate home theater
www.diysoundgroup.com
Floyd Toole has done some research into audio and speakers and has produce a few books in his time, which make for good informative reading (he also promotes constant directivity waveguides). His point about 'sound power' is what makes a speaker good, and constant directivity tends to deliver that:
Amazon product ASIN 0240520092
An interesting video here with him giving a lecture that is definitely worth a watch:
People like Dr. Earl Geddes and Wayne Parnham support waveguide speakers, and Waynes site is worth a look, with a white paper that goes into details about them (and others that are worth a read):
High-quality, high-efficiency loudspeakers with uniform directivity have been the Pi Speakers mainstay since 1980. From the constant directivity cornerhorns to the matched-directivity two-way speakers, Pi Speakers is the leader in the audiophile market.
www.pispeakers.com
There are probably discussions over on AVS that might be worth looking at for more info and opinions, like this one:
www.avsforum.com
I feel like I've said a lot but not really told you much. A demo is probably the only way to be sure, otherwise it's just opinions which quite often don't really count for much since they can all be different. As Zilch used to say: "More data, less w@nk"...