Neither the 2.4's or the 3.6's can match the depth of bass or the overall coherence of the 3.5's, and even with the demands of the 3.5's eq, the 3.5's are much easier for an amplifier to drive.
On the other hand the the 2.4's and the 3.6's are more refined from the mid-range on up, and more extended in dynamic range. The 2.4's have a tough phase angle and low impedance, the 3.6's have an easier phase angle but an even lower impedance. Both need an amp with real muscle.
IMHO, the 3.5's just might be the best used speaker value available today, just so long as you realize that they probably need an amp that costs more than the (used) price of the speakers, to appreciate all that the Thiel 3.5's are capable of. Still, it would cost many times the combined cost of used Thiel 3.5's and appropriate amplification to match, never mind do better.