I only drove a Pass X250.8 out of class A twice and it was just to see how loud it would be. Needless to say the answer was too loud.
Few observations
2- My move from Pass to high power class D was to get tighter bass and control the woofers with an iron fist. The do that so it met my expectations and preference.
This is what I'm interested to understand. Nothing aimed at anyone in particular, but the underlying reasons (physics, electrical engineering) for your observations are what puzzle me.
To stick with this example, the Pass 250.8 is biased to 25 watts Class A, and running it past Class A is not something that would be comfortable with the Spatials. So the Pass had far more power than was needed to achieve volume and control the low and mid drivers in a passive Spatial design. So it can't be the actual power (wattage) of the Class D amp that made a difference.
Yet, to generalize the case, I often see people say "I got a higher power amp and the bass improved."
With all of the volume generated by the first couple of watts, is the benefit of a 200 watt versus a 20 watt amp the speed of acceleration and deceleration in the higher powered amp? Does the extra power allow the high-powered amp to vary the voltage it is delivering to the woofer within, say, 100 nanoseconds while the 20 watt amp takes 300 nanoseconds? Would the ability to change current quickly then provide more punch (percussive force) and texture to bass compared to the slight smearing of the lower powered amp?
Shouldn't this be something that can be measured? I am not a measurement zealot, but it seems like there should be a way to gauge something like voltage delivery (knowing the impedances involved, the mass of the driver, etc.).