Which Component Has the Greatest Affect on Low-Level Listening

I'm looking to get out of HT 5.1 and go strictly to 2 ch.  I generally have music playing all day, often just sitting done to listen to certain tracks.  

I've read that "some" speakers don't sound "good" until high listening level, and also an integrated such the Luxman 505 don't sound good at low levels (is that the reason they include loudness?).

Which component, the amp or speaker, has the greatest impact on low level listening quality?