Upgrading from Thiel CS3.6 to Avalon

I don't believe it is an upgrade. You will lose the phase and time coherence and you will know it when it is missing. If you're at all like me, when I moved away from Thiel to Dynaudio for a couple of years, I moved back because I missed that pinpoint positioning of instruments and accuracy of timbre that the Thiels furnished.

Why not truly upgrade to 3.7s? Or Vandersteen 5As?

I've owned the CS1.5, CS2.2 and the CS2.3; you will find out that the Avalons' are much smoother, very coherent and projects a more stable image/soundstage. No forwardness or hardness in the midrange area YMMV...

IMHO, Avalons' are superior...

Overall, I have to agree with Stevecham. If you gave the Avalon's a thorough demo, and you know you really like them, that's fine. Otherwise, I wouldn't buy any new speaker. The ones you are looking at are just too expensive to take a chance on. Also, I would consider the 5A's, as well. Not surprising because Vandersteen is my favourite speaker.

I went from 3.6s to CS6 and to Salksound Soundscape 8. I am very happy with my latest purchase. IMO, The Salk is much better in every way.