IMHO what differentiated them was not db level but speed of the leading edge of the notes.
What Newbee describes is EXACTLY what you tend to get from an accurate subwoofer. It allows you to clearly discern different bass instruments as the timbre comes across clearly rather than just big booming bass. The kick drum does not bury or mask the bass guitar for example.
The slightest harmonic resonance in the bass (1 % distortion or more) simply clutters everything up...it means that many instruments are all producing stronger harmonics in the 60 to 300 Hz range where your ears are so much more sensitive that this effect dwarfs the proper balance of a musical bass.
The really big bass you hear from small cheap subwoofers is almost ENTIRELY coming from harmonic distortion - impressive but you can't distinguish anything anymore due to the "masking" effect of those higher distorted harmonics. It is akin to the sound engineer simply jacking up the 60 to 100 Hz range with an EQ to give a Britney Spears "hit me one more time" sound - nice but you don't need that on every track yoy listen to.
This can 'over-power' some midrange music, which can ruin the sound for me.
Well said John - this is EXACTLY the problem with small cheap subwoofers and the best remedy is to AVOID THEM altogether, which many audiophiles do (it also explains the "huge sub woofer integration problems" that most audiophiles face)
Of course it is understandable that nobody likes to fork out the similar $$ for a subwoofer to cover the last octave as they do for their main speakers => therein lies the problem and explanation for frustration with integration. Good bass is expensive - there is no free lunch and those who expect a free lunch from a sub rarely get musical bass.