A few comments.
I also listen at lower than typical volumes. I frequently have to fight with salon proprietors to turn it down when I audition new equipment. In my case, those lower volumes represent realistic volumes. Bach cantatas are seldom performed at 105 dB. So, Ralph, no worries! You did not confuse me by presenting the facts as dictated by physics and math.
My problem is that I played in several orchestras over the years and my wife was a singer. I've seen her singing in a Bach Cantata and FWIW 105 db is **easy** when the full choir is singing at a double forte (ff)! Having such exposure to the real thing (which is on-going; I operate a recording studio and play in a band), playing with peaks at only 75-80 db is good for background music when I am reading or cleaning up the kitchen but not if I am seriously listening. What if you want to play Wagner (Das Reingold, Decca, Sir George Solti conducting, side 6) or Verdi (Verdi Requiem, RCA Soria series, side one cut 2)?? 80 or 85 db peaks ain't gonna cut it- you need the unrestricted ability to play well past 100db without incurring artificial loudness cues (previously mentioned in prior posts) from the system.
With a low powered amp this means high efficiency and make no mistake. If you have 91 db, the is a moderate efficiency and although you may like what you hear, just keep in mind that you are not really hearing what the amp is about and for that matter the speaker as well and it just goes to show. Seems a poor investment to me, unless you are in a fairly small room or office.
But that's me- I figure if you are going through the trouble and the cash, might as well be able to really enjoy the music the way it was recorded. Others might differ on that...