I don't know where you been reading the S40's are hard to drive because that is ABSOLUTE CRAP!
They are EXTREMELY easy to drive,6 ohm nominal,NEVER drop below 6 ohms & are impedance corrected so as to have almost linear impedance phase...Your 52SE(which I have owned)are WAYYY harder to drive,4ohm nominal,3.6ohm low & 2 HARD phase swings...KEF,even worse...
They are EXTREMELY easy to drive,6 ohm nominal,NEVER drop below 6 ohms & are impedance corrected so as to have almost linear impedance phase...Your 52SE(which I have owned)are WAYYY harder to drive,4ohm nominal,3.6ohm low & 2 HARD phase swings...KEF,even worse...