Pass X150.5 vs. X250.5

Does not seem like an issue that will be solved by going from 150 to 250 watts (not much of a difference in dbs)and I think the 3As are fairly easy to drive and your room is not all that large. Is what you are hearing so apparent that it must be something other than a Class A versus B issue?

Where the meter sits is completely arbitrary, some sit at 12, some sit at 11, others wherever. What matters is if it moves. If it sits and does not move, then there is no leaving Class A. If it bounces all over the place then you need more power. The X250.5 is definitely a jump in power, but as many have pointed out it is doubtful that is your problem, it is most likely something else in the chain. Is the X250.5 a better sounding amp, to me yes, but if you have fatigue it is probably something else.

What is your source?

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.