Pass X150.5 vs. X250.5

Acurus makes a very important point and I agree 100%.
What is the location of your volume control knob?
Does your meter move from class A to AB?

Yes, Pass meters only reflect Class A to Class A/B (unlike McIntosh meters). if it is moving a lot, you probably are underpowering your speaker.

A Vandersteen 3A? In that size room? You might be underpowering, but I would think one is listening too loud if that is the case with an X150.5 - no? - I mean, that is a lot of power for that speaker especially a 87db /nominal 6ohms (I would think)

Ok, meter does not exactly BOUNCE, but the does move up from its static position at 9:30 to about 11:00 when it is at it's loudest. Doesn't really seem TOO loud, but that's a matter of opinion, unless it's causing hearing damage..... Anyway spoke to the folks at Pass Labs today and they said I COULD be running out of power, maybe the X250.5 is the way to go but borrow one first and see if that changes things. Sensible, those guys. They felt that meters hitting 11:00 was close to running out of power. I was kind of surprised at that, but who'd know better than them? Anyway they also suggested a change of wire to the upper section of speaker an another way of taming any harshness, but I don't think that would really help based on other cable I have used in the system. Just as an aside I originally had a pair of Aleph Os, but I sold them for the 150.5 to get more detail and dynamics, and that was exactly what I got. Another reason for looking into the 250.5 is that there are currently 2 in NJ on the list, and that's where I am, so It'd be very simple for me to buy one of them. Thanks for the info so far guys!

Once again, I think you are running out of power in class A mode, not total power. You indicate that when you turn it up, it gets bright and grainy (my words), this is indicative of these Pass amps that transfer out of class A to class A/B, in my experience. The 250.5 isn't giving you much more power in class A. I understand your desire and goals in moving from the Aleph series to these, but I think if you want to stick with Pass, you need to step up to more power in class A, even if it is less overall power in A/B to get the results you want, louder volume without the sound falling apart while achieving the more detailed and attachs that you felt were lacking in the Aleph series (with its more tube-like sound in comparison and its SET based design).

I still wouldn't rule out the room as a contributing factor. Some rooms can handle a certain volume or SPL level and exceeding that level can have consequences that aren't as noticeable at lower listening levels.