Kowkow,
I have been listening to CS6 speakers and have a friend who has a pair of CS7.2. He bought my Pass X350 and when he bought the CS7.2 he tried to drive it with them, while I used an X250 with the CS6. None of the amps worked well, although the X350 was OK with the CS6.
Before this I had a Levinson 331. Outcome is, that the Levinson 331 although it is only rated at 100W/8 200W/4 400W/2 had a better overall control than the X250. Later I had an ML No. 333 which was the best for my taste. (Remember that I am talking baouth the CS6 with is a much easier load than the CS7.2)
The X350 could not drive the CS7.2 of my friend to its full potential and the X250 was not capable to drive even the CS6 correctly. I am not saying that the music was not loud enough, I mean that with complex musical passages in classical music the amp lost its integrity. My friend then swithched to an ML No. 33H and it solved his problem but he needed to build a dedicated AC line for the amps.
If you like the sound of Pass amps, I think you should go with the X600. IMO there is no need to go for the X600.5 version only if your budget allows. BUT BEWARE! THE XA 100/160/200 AMPS WILL NOT BE ABLE TO DRIVE THE CS7.2. IT DOES NOT MATTER THAT THEY RUN IN FULL CLASS A, BUT THEIR OUTPUT IS LOWER AND LOWER AS THE IMPEDANCE DROPS...
The X600 is a great amp, but you should also consider the Jeff Rowland Model 8TiHC for example because its high current.
The CS7.2 is a reference speaker and it is wonderful, but it is almost impossible to find the right amp for them besides the X600, ML No. 33/33H, Big Classé amps, or Krells etc. The 33H is very-very conservatively rated at 150W, actually when it was tested it put out an amazing 225W/8 doubling down to 2 Ohms and they were unable to measure it at 1 Ohm because the AC line started to collapse... Levinson gives the output of their amps with both channels driven between 20Hz 20kHz while Pass gives the power at 1Khz (as usual). So as someone has already mentioned it is not only power which is important.
BTW, I currently use the Nuforce Ref 9 monoblocks with great results but I have not tried them with the CS7.2 yet. They have a damping factor of 4000 and rated at 160W RMS, and 350W for 20ms hold time at 8 Ohms. (analog swithching amps you may check them out at nuforce.com.)
Sorry for being a bit too long, but I hope this can help. Happy listening!