Actually JJ, you didn't really lose any bass/midbass. The speaker is still producing what it did before you raised it. Or to put it differently, its bass response/output is the same. What's different is that the bass part of the panels, when near the floor, were radiating into a quarter of a sphere. By raising the panels and (effectively) eliminating the floor plane, the (bottom of the) panels are radiating into a half sphere. So their output is now being spread over twice as much area as before, and more uniformly I might add, since there are no interference (reflected) waves bouncing up off the floor.
*** Its is changing the way your hear the mid and lower bass. Its not as ripe/full. Sounds less like listening to music live. The peaks and valleys have moved around in the room. ***
You need a sub in any case because the CLS's output drops to nothing at approx 35Hz. Unlike cone woofers, it doesn't produce lower-but-distorted frequencies. It just stops. A good reason to run them full range (with or without a sub), since nothing is gained by adding a high pass filter. Just let them do their thing.
*** Yes, there is something to be gained by a high pass filter. Macro dynamics/slam. Just try to getting any sound system to do justice to the dynamics of a live unamplified drum kit, piano, etc. ***
When adding a sub, the CLS's should still be run full range (as I already said) and the sub should roll off starting at no higher than 35-40 Hz! That's absolutely all you need to provide the CLS with that extra bit of low frequency extension and to guarantee a flat frequency response across the transition from the CLS's to the sub (i.e. seamless). If you are running just one sub (which is all you really need below 35Hz) with dipolar panels like the CLS, it's best placed between and in line with the panels. If it has a phase adjust, it's best set to 90 degrees, which is the best "phase fit" between the front and rear phase(s) of the panels.
*** That is where I have my sub. I don't have variable slope on my sub or variable phase, just 0 or 180. Full range, the CLS's now have a sharper roll-off. I have played with positioning and now have the sub more dialed in. I'm liking it more elevated now. I am leaving it this way for a while ***
You really shouldn't need a crossover if you have a self-powered sub with contour controls.
*** Just like the statements shouldn't need a high pass filter and mid-bass cone array. Adding the cross-over in effect give you a different speaker. In fact raising the CLS gives you a differently voice speaker A different set of trade-off's ***
10-12 inches is the optimum. Above that you don't get any more benefit.
*** That will depend on room size, placement, speaker rake, listening spot. Speaker height is going to affect what part of the speaker you will be hearing the most. More bass is coming from the bottom than the top. More highs from the top than the bottom ***
Bracing adds different benefits than raising. You can combine them or not. As a matter of fact, for a long time I had my panels braced only. I unbolted the electronics chassis from the panel and just set it on the floor right behind. Then, with the panel on just two spikes, I attached one end of a five foot long, 3/4" dia. aluminum tube from the rear center of the top rail straight back to the wall behind. That sucker couldn't sway even a millimeter! The transient response and imaging were just amazing . . . . .
*** Agree the benefits of bracing are entirely different from speaker height. I would find it hard to believe the would be any trade-off from rigidly bracing the panels assuming you are not introducing a large reflective surface behind the panel. Adding a sandbox to the braced stand could add another plus to equation. ***
Good luck!