If you're enjoying the 3.6's in your current system, I wouldn't look at Vandersteens. Both are outstanding speakers but at two different sides of the spectrum; Vandersteens tends to be slightly dark and Thiels slightly bright, neither to the extreme. I would think that you probably have a system that tends to balance the Thiels, which means that with the Vandersteens everything will be too dark.
Thiel 3.7 is a major step up from the 3.6's.
Thiel 3.7 is a major step up from the 3.6's.