Why are high efficiency speakers preferred for low volume listening?

Thanks, @ditusa  , I am going to have to print that because my eyes are so bad I cannot read that on the screen.

I listen to my apogee duetta 2 speakers at low volume with no loss of detail, it's quite enjoyable.

I have been using 16 ohm 101db speakers driven by 35 watt and 130 watt amps for 47 years. 

During that time, I have noticed that the aging of the components matters a great deal. I recone and demagnetize the drivers regularly. Capacitors start to leak within about the same time, they get upgraded and replaced. Etc. 
 

theaudioatticvinylsundays.com

Sensitivity is a measurement of steady noise or tones and seeing how loud it is at 1 meter away. Has absolutely nothing to do with the quality of sound. 

But higher sensitivity speakers are often made with quality audio in mind, and low sensitivity are often made for cheap mass production, so people correlate "high sensitivity" with good sounding audio. In reality, there are many factors of driver and loudspeaker design that can make a speaker sound great at any volume level. 

My Kef blades needed volume to sound dynamic with my 300 wpc hegel so imagine my surprise when I tried the mc611’s and with the power meters bouncing around .6 of a single watt I was listening to tuneful bass and multiple layers of tones I previously had to really turn up to get? I almost never exceed 6 watts peak output yet the sound is completely unrestricted. Listening to delta cream, the black keys while typing this and am stunned by the dynamics at around 1-3 watts. Can anyone explain