What Difference between Pass X150.5 and X250.5?

Eril, this can be a little confusing unless we define which generation of X-amps we are talking about. In the original X series the X-150 became the X-150.5 when Pass decided to add the blue meter to the front of the amp, which the X-150 lacked. Otherwise, the amp was exactly the same. I'm assuming your question is regarding the new generation of X-.5 series, which is a major revamp of all the X-series amps. All the new x-.5 amps sound terrific in their price range. What you get as you go up in the series is not just more power, but higher initial single-ended class A biasing for certain amount of watts. This is followed by a number of regular class A watts untill the amps go over to class A/B. Because of this the 250.5 will give much more of the taste of the Pass Labs X/A series amps. The dynamics, slam, transparency of the old X-series with the warmth of timbres and organic/liquidity often heard in tube amps. I have the 350.5 in my system and enjoy its virtues on a daily basis. The 250.5 will give much more of the above stated sonics then the 150.5, even though the 150.5 is terrific at its $ point the 250.5 is just that much better. Hope this helps.

Thanks Teajay.
I am currently using a Cairn Integrated Amp (first 10 watts in class A) with my Jean-Marie Reynaud Evolution 3 speakers. 88db sensitivity - easy to drive but do better with high current and high damping factor.
The speakers are well banced but a tad soft/warm.
I like the Class A sound better than any AB or valve sound I have yet heard and I thought the new Pass X-5 series was a good potential match.

I assume the new Pass ".5" series of amps was only from the X250 and up, i.e. the current X150.5 untouched correct?

Teajay, you say: "X-150 became the X-150.5 when Pass decided to add the blue meter to the front of the amp, which the X-150 lacked. Otherwise, the amp was exactly the same." The Pass site seems mostly to confirm this, but they do give one measurement which is significantly different from X150 to X150.5: something called "Balanced CMRR" is given as " -85 dB @ 1 kHz" for the X150, but "approx. -70 dB @ 1 kHz" for the X150.5. This suggests that the amps do in fact have some significant internal differences, not just a meter on the front...unless you have heard otherwise from Pass themselves?

Calanctus, I have no information that would put in doubt what you stated on the Pass Labs website. I remember a long time ago that I talked to someone in Pass's office who said their was no sonic difference between the 150 without the meter compared to the 150.5 with the meter. The new 150.5, along with the whole new X-.5 series, is a different matter entirely. Remember, Eril, its not just class A biasing in the new series, like your Cairn amp, but single-ended class A biasing for certain amount of watts before going into regular class A. This gives some of the sonic virtues normally associated with tube SET amps. The 250.5 lives in a different sonic world than your Cairn Intergrated amp, which is great for its cost, but is not is not really competitive with the 250.5. But remember your comparing amps that are a least $4000.00 different in their prices. In this case more $ really brings a much higher level of performance, often more $ doesnot = better.