recomending power to speakers

Try the 4 ohm taps first before you throw money at it. You also might have the amp checked out depending on its vintage as tube amps do require periodic service to replace caps, tubes, and so on.

I used a Levinson 27.5 with Thiel 2.2 CS speakers and never had a shortage of power. I believe this amp, or a Threshold pure cl
ass A model (SA3 or better), will work fine with your speakers.

These amps would do the trick with 200 triode watts per channel:
http://cls.audiogon.com/cgi-bin/cls.pl?ampstube&1132177886

If you want to stick with tubes look to a high powered VTL monobblock amp. A good friend, electrical engineer, used a pair of VTL tube amps for his Magnepan 3.6 speakers which require a TON of power to make them sing. I think they were the MB225 which run in triode mode. If you do acquire a VTL and it has switching between triode and pentode mode NEVER flip the switch when the amp is running; you may blow it.

i would keep the arc and ditch the thiels. go vandersteen, castle, klipsch, or one of many more musical(and 60w) friendly models.

Ditch the ARC. They are dry and lackluster with most speakers. If you insist on tubes go with high powered BAT, VTL or Manley. Good solid state amps for your Thiels are Pass or Classe. Krell and Bryton present the same dry sound as ARC so avoid them.

Speaking to Thiel they said that they mostly use Krell amps in their listening rooms. I know Krell is known for treble sizzle and a analytical sound...so it wouldn't be the first choice in my book. A better balance might be a sonic frontiers tube amp. the power 2 or 3? With the 1.5's you'd be fine with the SF power 2. It's a small speaker and if you're not in a huge room 100 watts will go a LONG way.

Maybe a pair of Odyssey mono extreme se's would fit the bill; give Klaus a call he may even have some demo or b stock which can save you some money for better cables or whatever else you may need.
Also the 20 year transferable warranty is a good selling point when the upgrade itch hits again and Klaus is one of the good guys in audio;like Ralph from Atmasphere.
I agree with the tube amp suggestions thus far and add Audio Valve from Germany.