Well engineered music *is* designed to be played with a flat response. My speaker system is audibly flat and almost all stereo and digital era recordings sound perfectly balanced without having to touch the tone controls. The same is true of most 50s and 60s jazz, and 1950s popular music of all kinds. The area where engineering doesn't follow the standard is in some modern remasterings of 70s rock music, a lot of contemporary pop music and rock... and just about all hip hop and electronica (which have boosted bass). I don't listen to a lot of the problematic music, so I can put my entire media server on random shuffle and hear about two years worth of music that doesn't require any adjustment from flat.