Marco,
Thiel speakers are very power hungry. The sensitivity is given as 86 dB but for 2.83V/1m, (2,83 is the square root of 8, normally manufacturers use this if the speaker's impedance is 8 Ohms.). Because of the fact that the CS6 has a 4 Ohm impedance, the actual sensitivity of the speaker is 3 db less: only 83 dB. This is a really low value and if we add that the minimum impedance is near 2 Ohms then there is no question anymore: we need lots of power. The actual need of power of course depends on the room size and our listening habits too, however my experience is that 200W/8, 400W/4 Ohms is the minimum these speakers neeed in ANY room setup. I had a Mark Levinson No. 331 before and it has almost ran out of its reserve and was not capable of driving the speaker to its full potential. I am not talking of not being loud enough, of course I could not pump up the volume to the max. even with the 331, but at that the same volume level the bigger amps were much more relaxed and had better control and did not lose anything from their imaging.
I tried the No. 331, No. 333, Pass Labs X350, X250. The best were the 333 and the X350. The X250 is hardly enough, sometimes I feel that the 331 may has better control, but the X250 has the power and never collapses.
As far as tubes are concerned, Thiel recommends approximately the double of the SS power when you use tubed gear. The VT 100 is a great amp and sounds good, however I doubt that its control is enough, no matter how small the room is. Of course this is only my interpretation... The only tubed amp that I listened to and offered tremendous power was the VTL MB 1250 Wotan and the VTL Siegfried. The latter was the best tubed amp I ever listened to, faster and more dynamic than most SS amps. In your search for the right cables you might as well give a try to the Pass X350, it definitely worths considering.
