In the "Review of two recent recordings"
https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1593494841
Steve Deckert used 4 different headphones and said:
"Let’s just grab a third headphone.  This one is complimenting the presentation the best overall while each of the other ones did certain things better."
Then trying a fourth pair:
"This last pair I am at the back of the pool and everything sounds completely real.
     If I’ve learned anything tonight it’s why serious headphone listeners have so many different pairs."

This has me wondering:
Considering the cost of modern headphones, would it be money ahead for the listener if Decware were to build a headphone amplifier having one amp chassis with several circuits, and owning only a single set of headphones instead of multiple phones.
A listener could then plug into one of four or maybe five jacks to get the sound he wants. Or possibly the chassis has only one jack with a rotary selector switch to choose between the circuits.
Perhaps they would not need to be complete circuits. The effect may be achieved if some resistor or capacitor or something were made multiple and placed on a selector switch.  

I think there's more to it that would end up being more complex than just switching a toggle between different headphones. . . .

I've ended up with there different systems, and a headphone amp in each, and the three headphones I have each work best with one of the amps. Not an ideal situation for most I'm sure, but works just right for me.

Headphone amplifiers are nothing but a device to boost the audio in order to produce a more realistic, crisp and clear sound.