My 20.7s play at low volumes really well. It did take a LONG time for them to break in to play at low volumes really well.
(the main issue was dynamics. low level material Like in Classical music, would 'fall off' the stage.. and it took months and month of play to have them not do that. The break in might have taken a long time because I generally play at low volumes all the time. But I am playing them all day every day...