What creates the effortlessness in sound reproduction?

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*

"Effortless" for me is context-dependent, including the old trick of turning off the lights and listening with candle light only. Turning down the volume a bit, so I am dragged into the music rather than having it pushed at me. If I'm stressed, music sounds worse. So it is a matter of the listener not just the "objective" system. Add all the good advice above, like good source, preamp and amp, efficient speakers, etc. Avoid over-damping the room. Maybe consider a distributed bass system if it blends well with the speakers. - The Cream reunion album, mentioned, is very good on vinyl too.