Perhaps a frequency bump in the 4-6 kHz range that adds “edge” to the sound and attracts attention at lower volumes.
Same can be easily accomplished with other good quality less efficient speakers like say Sonus Faber, KEF or even Ohm using DSP or equivalent parametric eq.
I’m listening to a pair of SF Concerto Domus at low volume that way using Roon DSP as I type. Might be fooled into thinking they were high efficiency horns with eyes closed.