Just stumbled on to this discussion.
I have a pair of 2.3s, and my friend 3.6s. As people have said, good clean power with the ability to effortlessly drive 4 ohm (2 ohm ideally) speakers will make a dramatic difference. When matched well, the Thiels are really special.
We had some success with older Krell amps and almost any age Classe (as others have noted). The Classe's really match well, being able to really grab hold of the lower frequencies, giving tight, articulate, but full bass. Even an older Classe CAP151 integrated was a great match with his 3.6s in a modest size room.
Someone mentioned that NAD doesn't match well. Hmmm... that reminds to try my NAD M2 (digital power dac) with my 2.3s that are in storage because my listening space is a little small at the moment. The NAD M2 completely blew away my Peachtree Nova 125 amp with the bookshelves currently in my system.
Agree, Thiels really perform way beyond their price point. Buying older models in good condition is value beyond belief.