What creates the effortlessness in sound reproduction?

I'm sorry for my ignorance but I am not sure I understand this correctly. Do you mean that in an experiment of several systems which are playing at 100dB, some system will be louder than the rest?

@quanghuy147  No. Some systems will **sound** louder. This is because higher ordered harmonics are used by the ear to sense sound pressure. If a system is making more of them than a 2nd system, that 1st system will sound louder even though it isn't. In fact this is so profound that the 1st system could be a good 15dB quieter and still sound louder.

Eliminating intermodulations and higher ordered harmonic distortion is the key. 

Larger drivers being slower is a misnomer. Often smallish drivers are wrongly claimed to image better, sound quicker, etc. It's mostly attempted justification for a lesser rig. Listen sometime to how much distortion a 6.5" woofer puts out in comparison to 15". I prefer not to introduce that level of distortion into low end performance. :)
As usual, YMMV

+1 to Doug

I find 18 inch Scaena subwoofer to be fast enough to match Lansche 4.1.

The most effortless speaker that I had heard is vintage Western big horn with  field coil magnet.

Because of high efficiency you need less than 20 watts of power to fill the big room.

The biggest problem though I believe is the lack of good recordings. Let me mention one that holds for any sound level - Cream reunion live at the Albert Hall. Bluray.

*S*  What I've appreciated from and by y'all is the 'brand-less' and 'item-less' qualities of this forum....

Don't tell me 'with What' you're 'using'....speak to me about What you seek.  What are you listening for?  The qualities, the impressions, the nuances...

Paint me a picture....don't brandish an advert.  If there's something 'specific' that you mention, we can always find a means to exchange that and those details...

I realize that this may strike as 'Pollyann-ish'....but, at least, for awhile, Here....

It's been mostly avoided...and I'll thank y'all for that. *S*+!^5's*all that....

(I'll give Eric a pass, though....he seems to live in a GIK padded cell, and I can relate...;)...

...I can only hope he realizes that I'm kidding Him Big Time...*G*)

Respect and admiration can begat parody and pun....and I'd be remiss if I'd didn't act 'to form'...*S*