Pass 150.5 vs. Pass 250.5 ?

Jond is right. At least partially. These Electra's can be driven even with 300B SE amp. I tried it at home with Audion 300B and I had quite good result with it. Very nice and open mid-range with quite good bass extension and excellent timing. The problem is that I am looking for much better and more authoritative bass control - one that I had with Bryston 4B-SST (which on the other hand was a bit closed in the mid-range). Therefore, I am formulating my question now a bit different: would I get these virtues with Pass Labs X-150.5 ?

Dejanm, excuse my ignorance, but I don't get it.
You say that the speakers are efficient enough to be driven by a 300B SET amp, yet you mention you liked the bass control of a SS amp that puts out hefty 300w/ch into 8ohms. You want a 150w/ch amp to have the same bass control?

Audphile1 I was making a general comment on the efficiency of JMlabs designs, and since floor standing speakers are typically more efficient than monitors it stands to reason that if my monitors are efficient than a floorstanding model from the same manufacturer may be even more efficient. My comment on the 150.5 versus the 250.5 simply takes into account the commonly held, and with good reason, belief that a lower powered amp from a given manufacturer will sound better, usually sweeter and more pure, than a higher powered one. Given that, plus the fact that I've read many users who state that the 150.5 is a better sounding amp, even to the point that a tech at Pass said it to someone as well.

@Audiophile1

I said that I would like to have more bass control than SE valve 300B provided - something that heavy SS amps like Bryston are providing. Whether Pass X-150.5 will provide the same class of bass control is something that I really do not know - that is actually the reason for my question on this forum. In addition to that, Pass is not quite the same as Bryston, meaning that maybe its 150 W can produce the same low level magic as 300 W of Bryston. Although, maybe it will not be the case ? Does anybody have any concrete experience with this Pass amp ?

I was listening the older model X-150 connected to Thiel Cs2.4. Very unpleasent speakers to drive - they need a lot of current. It was a direct comparison with Mark Levinson 331 (source was also Mark Levinson 390S directly connected to one of these two amps with XLR HMS cables). Speaker cables were also HMS. And ... Pass X-150 outperformed Mark Levinson 331 in every respect. But Mark Levinson 331 is "only" 100 W/ 8 ohm.

So I was thinking if it did it with ML and very difficult speakers, maybe it will do the same magic with my Focals compared to Bryston .... Or another analogy shoud be taken: it did it to Mark Levinson because it has more power ...

That is the question now ....

I tried both 150.5 and 250.5 with diva utopia. Both drive it to adequate level. 250.5 has quite a bit more detail. The treble is slightly hotter with the 250.5 and the base was a little disintegrated with the midrange ( probably due to speaker side firing woofer). X150.5 is less detailed and less dynamic (comparatively) but overall a more coherent and musical presentation. Room is about 25 x 16 ft. X350.5 is better than both which is what I use now.