Gnobber:
I wouldn't say that the imaging or the soundstage was necessarily better with the 2.4's. More like you were listening through a thin sheet of fabric with the 3.6's by comparison. So, I guess that would also mean that to my ears the 2.4's were brighter and less laid back. And by using that term for the 3.6's, I mean laid back only by comparison to other, newer, Thiels. In general, they are not what I would call a laid back speaker. And from what I could tell (not being able to do a direct A/B with identical systems), I did not think that the 2.4's had smoother treble. In fact, I'd say that my ears told me just the opposite. The 2.4's are great speakers. And they really wow you with their scalpel-like precision. Notes end exactly when they should. The definition between instruments is palpable. Overall, I liked them a lot. However, I liked the more full sound of the 3.6's, and I find the 3.6's to be a tad softer on the high end. Another factor in favor of the 3.6's is that the 2.4's don't feel like they are moving as much air. They just didn't have the same degree of weight to them, when the music calls for it.
Drubin:
Yes, I agree that the 2.4's are more forward sounding than both the 1.6's and the 3.6's. If you feel that the 3.6's take a bit of the edge off of your music, then the 2.4's are a better match. Conversely, if your system needs to have the reigns pulled in a bit on the high end, and needs a little beef added, then the 3.6's may be the ticket. I will say that the midrange focus on the 2.4's clearly exceeded that of the 3.6's. While I consider the 3.6's to have full, balanced midrange, by comparison to the 2.4's, the 3.6's sound slightly warm and fuzzy. With my system, and in my room, that is not such a bad thing. But if you had a fairly neutral system in an acoustically non-reflective room, the 2.4's (especially with a sub) would probably make you smile a little harder than the 3.6's.
All in all, they are both Thiels, and probably sound more alike than they do different.
Hope this helps, Tom.