The bigger Thiels will not sound great unless fed with a lot of power. My experience with the 3.6s is that, when driven by a less than macho SS amp, they can sound thin. Feed them a good 300-500 watts and the sound becomes much fuller.
Thiel 3.6's vs. Vandersteen 3 sigs
Looking to upgrade. Currently have Vandersteen 2ce's which sound great, but have slight bass. So, I had to get a Velodyne FSR 12 to compensate, but this is not a really good match, I know. Anyway, I miss the bass that my old Thiel 03a's had by themselves. I'm guessing that Thiel 3.6's may cover all bases well. I'm not familiar with the VD 3 sigs, just hoping that they would cover the low frequencies better. Of course, the other option in to get the Vandersteen sub and keep the 2ce's. By the way, the speakers are powered by a Moscode 600 with a Rogue Audio 66 Magnum preamp. Any suggestions?