Hi: I've owned the 301 and also listened to the CA 150 extensively. In my opinion, the 150 is far to weak for your Theils, which are not the most efficient speaker. I heard the 150 vs 500 on a home theatre system with ML Requests and the 150 couldn't handle it at all. Unless you are going to biamp everything, go with the CAV 500. I have heard that amp and it is wonderful on big speakers or inefficient speakers, lots of power and simalar sounding to CA 301. The 301 has got lots of power for any speaker, the 401 might be overkill, but if you've got the coin, why not.
Also, consider 2 CAV 500s in vertical biamp on everything, as this might be better than the 401/CAV 500 combo. You might also want to look at a pair of Theta Dreadnaughts 5 channels, as they are IMHO are even better than the Classe (Classe has more power and is slightly sweeter, whereas Dreadnaught is dead flat and very revealing of good (or bad) source. At $6K each the Dreadnaught are a good value and I would put them, the Classe CAV 500 and the new BAT 6200 on your short list. And then there's that new Jeff Roland 6 channel ...--Lorne