What creates the effortlessness in sound reproduction?

Hi Huy,
Talk to them. They'll help you get set up. Have a budget in mind. :)

They are really pros at this.  I'm an amateur by comparison.

Best,
E

As geoffkait indicated, but, in two words, dynamic range. Every listener, should have some experience, to listen to live, unamplified music, to get an understanding of what dynamic range, really is. ( real musicians, in a real space ). I am speaking of music and sound, as dynamic range is also associated with  vision ( photography.and video ).

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.