Pass X150.5 vs. X250.5

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.

Interesting theory about the room. You could be on the mark there as there are absorber panels between the speakers on the front wall,and a panel at each first reflection, but nothing behind the listening chair and nothing on the ceiling, although one can go to far there too. Thought the live end-dead end theory was at work, but I'll try some absorption in the back too. Also understand where you are going with the class A amps. I was thinking in terms of total power, not class A power when I thought about the 250.5. I'd probably need at least an XA 100.5 to make it work in class A, but that is WAY above budget.

I would not rule out XA60.5s being able to drive the 3As to VERY loud levels - but, still expensive.

I agree that you should look at the room. IME, some adverse room effects, particularly in the high frequencies, are inaudible at lower volumes, but quite noticeable at louder volumes or during peaks.

Here is a 10 second test: Standing in a couple different places in the room, clap your hands loudly. What does the decay sound like? Is there ringing? You may have a flutter echo that is bothersome only on peaks.

If you do have a room problem, then adding diffusion at this point may be a better idea than adding more absorption, but both should have a significant impact.

Bryon

Bryon is right IME. Try diffusion on the back wall versus absorption.

Ceiling though is a nice area to address as it too is a first reflection point. But ceilings are a bit more difficult from an aesthetix stand point.