I think the Contour S5.4 needs to be played moderately loud (preferably in a big room) to come alive. Even more so than my 1st gen C2. Same for the older C1 and S1.4. Maybe the C4 too, but I've only heard it in rooms that were too small for it. My Focus 160s are possibly better balanced for low volume playback than those speakers, but they still sound better when played above 75 dB average level.
I have never had the pleasure of hearing the S3.4, but the measurements I've seen show a little bit of "smile" shape in the frequency response, which is like having a little built-in loudness compensation and would make them better at lower volume than the S5.4 which is pretty flat.
HT: Dynaudio C2, Contour S CX, 2x BM14S, Aperion surrounds, Simaudio Titan, Marantz AV8801, Oppo 103, Linn Majik DS, and a Pioneer Kuro
Stereo: Dynaudio Focus 160, Simaudio W-5 LE or Luxman M-600A, Linn Akurate DSM, 2x Rythmik F12G
Other interests: motorcycling, skiing, being active