If the source has large and sudden dynamics, when low powered amp is driving lower sensitivity speakers, and they are lower impedance speakers (a hard combo for any amp) the amp will not have enough reserve to supply the juice to the speakers for the dynamics, especially bass which is the most power hungry frequencies.
My Office System: My Little Luxman Tube Integrated:10 wpc at 6 ohms
https://www.luxman.com/product/detail.php?id=33
is driving Vintage AR-2ax, 91.5 sensitivity at 8 ohms.
https://stereonomono.blogspot.com/2014/05/acoustic-research-ar-2ax.html
very nice combo, however I need to turn the volume up further than most amps I have owned over the years, and while enjoyable volumes are produced, I would not expect great dynamics out it this combo.
Previously, driving Wharfedale Diamond 225’s, sensitivity 87db at 8 ohms
https://www.stereophile.com/content/wharfedale-diamond-225-loudspeaker
the Luxman Volume had to go even higher.
It also sounded good in this room, but you have to know/acknowledge the limitations.
I bought the AR-2ax for nostalgia for my Garage/Shop system (I had them in college). they sounded soooo good, I moved them to my office, gave the Wharfedales to my son, and bought a 2nd pair AR-2ax that I am restoring for my Garage/Shop system.
AR gives some power formulas here, page 12, magnify