The volume issue is simply that they are voiced at realistic music levels. The equal loudness contours effectvmeans that relatively speaking ATCs sweetspot (where treble and bass are balanced) is a little higher than your typical smilie EQ speaker.
http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/eqloud.html
Comparatively Harbeth, B&W and many others are voiced so that they have more bass and work better at lower volume. Of course, excessive bass will ruin the balance of sound at louder levels but most speakers aren’t capable of live loudness levels anyway. This is the pro aspect of the ATC design - the drivers play cleanly and without stress at relatively much louder/dynamic levels than other speakers.
http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/eqloud.html
Comparatively Harbeth, B&W and many others are voiced so that they have more bass and work better at lower volume. Of course, excessive bass will ruin the balance of sound at louder levels but most speakers aren’t capable of live loudness levels anyway. This is the pro aspect of the ATC design - the drivers play cleanly and without stress at relatively much louder/dynamic levels than other speakers.