Pass Labs amp choice for CLS - What would you do?


After much reading and soul searching I have decided to upgrade the amp on my CLS speakers. I can buy a used X350.5 (current generation) or a pair of X600 mono blocks (previous generation - can't afford the X600.5) for a similar price. Is the .5 model change significant? There is no way that I can audition/compare them on my system, so I will have to take a leap of faith. I know I can't go wrong, but what would you do? And what pre-amps should I be looking at?
dchazen
Thanks for the feedback. As I continue to talk to people and read it is becoming clear that the .5 model change is important. The CLS likes a lot of power and the impedance can dip down to 2 ohms, so the amp has to be stable. I understand that the original XA series had issues with handling low impedance speakers, but this was corrected in the .5 series. The pure class A power of the XA is supposed to be phenomenal sounding, but the class A watts are more expensive. On the other hand, I have read that you don't need as many class A watts to drive the same speaker. I have seen comments that the X350.5 and the XA100.5 are the "sweet spots" in the Pass Labs model line up in terms of power that can handle most speakers and bang for the buck. If the choice is between the X350.5 (MSRP $11K) and the XA100.5 (MSRP $16K), then what would you say?
Dchazen, if it's in your budget, in my opinion, you should go for the XA-100.5's. If you read my review on the XA-60.5's for the details regarding their sonic beauty, you will see that they are on a higher musical level then the X-.5 amps and yet now have the current/watts to drive virtually any speaker. I would also suggest you give a call to Mark at Reno Hi-Fi with any questions you might have and he's great to do business with. You could set up a 30 day home audition, if you don't keep the amps you pay for shipping back and a very small restocking fee.
I also recommend the XA100.5. In my review on Audiogon, I compare it to other Pass Class A amps that I have owned, and it is by far the best of the bunch and it can handle difficult loads. You will also have the advantage of mono blocks over the stereo X350.5. I have not heard the X350.5. Mark @ RENO might even have a good demo listed. I bought mine from him and it was in excellent condition and I saved some money. Two audio friends heard my XA100.5 driving my Egglestons and both called RENO and ordered pairs.
I'd also recommend XA-.5 over XA or X-.5. You may not have to get XA-100.5 to get adequate power for your speakers. For example my XA-30.5 clips at around 200W at 4 Ohm load. It's driving a pair of JM Labs Electra. You may or may not need more power for your CLS, but keep in mind that Pass amps are rated very conservatively.
"If the choice is between the X350.5 (MSRP $11K) and the XA100.5 (MSRP $16K), then what would you say?"

XA100.5. But don't rule out the 60.5 or even the 30.5 especially if you don't play your music that loud and I'm guessing you don't with the CLS. Electrostatics are capable of such great microdynamics, an XA.5 should be a great match for them.

For a preamp, Pass's XP-10 or 20 would be a nice match and if you favor tube pres, Conrad Johnson is my favorite. As I'm typing this in my office right now, I'm listening to a CJ CT-5 driving an XA30.5. I've had no desire to change this combo in my office.