lars - a few thoughts. I have rather recent acquisitions of both CS5i and CS2.4, but not much actual experience with either of them. I’ll jump to my conclusion first which is that the 2.4 might well suit your needs better due to what may be your fairly small space.
The CS5 has individual drivers, which at 8’ don’t integrate their soundfields very well. Also, the primary advantage of larger speakers is to fill larger spaces with deeper bass and higher amplitude. The 5 will do that only if you have the proper amplification to drive them, which as you’ve read here is a very big deal. The 2.4’s upper coax tolerates listening at any distance without compromise. The listener is freed from the triangulation necessary for individual drivers to integrate.
Another trajectory is that as Thiel and in particular Jim learned more he developed more sophisticated drivers. The CS5’s only driver from the ground up is the UltraTweeter. The ’i’ designates ’improved’ and adds copper motor shunts to the 3 woofers for significant bass improvement. The Focal lower and MB/quart upper midranges are very good stock drivers having none of Jim’s innovations. I’m saying that the 5 is earlier on Jim’s journey and as such the drivers are more ordinary. But, if you are filling a large space at full amplitude, the 5 puts out much more sound. Unless, of course, you can’t handle the power in your room.
There is another aspect that matters a lot to some people, myself included. The CS5 has true sealed bass. The transition from midrange to bass (down to 10Hz) is true first-order phase and time coherent bass. It acts like a real acoustic instrument in your space. The 2.4 is a very well executed reflex bass system using a passive radiator. The transition from the upper bass (woofer) to the lower bass (passive) at 24dB/octave (4th order) introduces a full cycle of delay in the sub bass - more than 20 feet behind the upper bass. That alignment has become acceptable in nearly all speakers, even costing $6 figures. But it is less authentic than first order sealed bass.
My studies in audio neurology suggest that the brain builds audio understanding from the bottom up. And therefore inserting the timing discontinuity between deep and mid bass consumes effort to decode and suspend judgement regarding the error. Again, the 2.4 bass is about as good as reflex bass gets, but it’s still reflex bass.
The 2.4 is easier to drive than the 5. Reflex bass eliminates current draw in the deep bass because the bottom octave is supplied via tuned mechanical delayed resonance, not a driver motor.
A pair of 2.4s might be found at under $1K. And a stellar and affordable upgrade path exists because there is no electronic crossover between the midrange and tweeter. The 5, on the other hand has 4 electronic crossovers, each far more complex than any of the 2.4 circuits because the later 2.4 drivers behave better, needing less correction than those in the 5 / 5i.
Tom T