Regarding these amps that don't have bass oomph and create the perception of speed and cleaner mids.
Are these amps you refer to (Cyrus/Leema) with electronic (chip) volume control and EQ instead of classical analogue potentiometer and discrete preamp board? If so, they have unlikely implemented loudness compensation at quiet levels, or perhaps they've chosen not to use it excessively.
As you know, human hearing is insensitive to bass frequencies compared to midrange, so it's common practice to implement loudness compensation in amps. If the amp doesn't have a loudness switch, it could be implemented to taper off from 100% at 6 o'clock position, to 0% loudness compensation at 9 o'clock.
Many amps are bass heavy untill you turn beyond 9 o'clock, anticipating quiet music up to that turn position, yet the amp is already screaming loud because the input sensitivity for the sources is too high (sub 200mV). In effect you get unnecessary bass bump of as high as 10dB at normal listening levels. So only way to fix this design flaw (or shall I call it a marketing feature), you need to adjust the input sensitivity trimmers, if available, or use something like Rothwell attenuators.
I've seen most if not all Stereophile measurements of Cyrus amps. They measure pretty flat, no lack of bass or highs. And the power supply is always chunky on Cyrus kit. So I have this theory it's about how loudness compensation is implemented creating this perception you speak of.