I just auditioned the 2.4 in my system. I currently own the 2.2s, but have auditioned the 2.3s and 3.6s extensively in my system (and always prefer my 2.2s, so I keep them!) I found the 2.4s to sound more similar to the 3.6s than to the 2.2s or 2.3s. The 2.4s are far more full-bodied, with more natural warmth than the 2.3s. The 2.3s however were quite a bit more laid back and natural. It's too bad they were rather sterile and colorless and lacking in warmth. They were at least sweet. The 2.4s are more forward and brighter by quite a bit, very much like I remember the 3.6s sounding in my system. Their bass is superb - deep and tight. However, I found its bass volume limits rather sooner than I expected. I have yet to reach the bass limits with my 2.2s, and never did when auditioning the 2.3s or 3.6s. But what Thiel is calling an 8" woofer in the 2.4 sure does look like a 6 1/2" to me. Smaller than my 8" in the 2.2s. The midrange clarity, however, was to die for in the 2.4s, but it is rather forward.
Which to buy? Depends on your amplifier. If you have a truly high-end, very high quality, high-powered amp, I'd buy the 3.6s. If you've got anything less than that in an amp, I'd buy the 2.4s - they are much easier to drive. But make no mistake, the 2.4s are as ruthlessly revealing as the 3.6s. None of the forgiving nature of the 2.2s, which is probably why I always end up preferring my 2.2s over any of the others I listen to. But if you've got the right stuff, the mid range of the 2.4s is simply spectacular.