mo' better bass: any substitute for watts?

Correct. In the old days, some amplifiers had a 'Damping' control, which was a potentiometer that allowed you to adjust current feedback (not voltage feedback). Essentially, this allowed you to get a better match between the amp and speaker.

This was at the time that the Voltage Paradigm was evolving. Once the ground rules were laid out, the 'Damping' controls disappeared- everybody just used a lot of feedback and called it good. The problem is that feedback itself functions at low frequencies (bass region) as a dynamic compression device. You simply aren't going to get good bass (or **as good** bass) if you are running a lot of feedback, even if your system is matched within the Voltage Paradigm.

This is why a smaller amplifier that has little or no feedback can often seem to play better bass (more impact, more definition, more articulation) than larger 'powerhouse' amplifiers that would seem to have it all over the said smaller amplifier. Of course, such an amplifier itself has to be able to operate properly with the speaker in order to revel these traits, but its not that hard to find speakers that are compatible and capable of delineating the differences between amplifiers that I defined above- the speaker *does not* have to be full range.

I find that class of operation plays a role too- class A amplifiers will have more authority; as you move more towards class B (AB1 and AB2) the authority (especially at low volume levels) goes away.

So- to play bass well, power output is irrelevant, instead the amplifier ideally is low or zero loop feedback and class A, given that such an amplifier also works well with the speaker being used. This of course assumes that the amplifier does not have a low frequency cutoff that interferes with bass reproduction.

Atmaspere ;
Do these characteristics ,

"the amplifier ideally is low or zero loop feedback and class A"

apply to all types of amplification ie. tubes , SS and digital ?
What gives tubes the "punch and body" at lower volumes ?

Yes, tubes and transistors; the jury is out on Class D as it inherently is not Class A.

Tubes generally are usually operated closer to Class A than transistors usually are; most transistor amplifiers are biased at such low idle currents that its driver transistors (not the output transistors) are actually what is driving the speaker at low volumes. Tubes are inherently more linear than transistors, especially triodes, so tube circuits tend to be simpler and operating with less feedback, in fact I think its safe to say that the majority of triode amplifiers don't run loop feedback at all.

So your "punch and body" is coming from the reduced levels of negative feedback and the additional authority gained by operating at or near class A.