Mine is better with Loudness off
I've finally had a chance to setup and play with my S5 and I really like it. The bass was a little boomy so I looked through the manual and found that unlike a "normal" Zone Player like the ZP120, the S5 has Loudness on by default. "The loudness setting boosts certain frequencies, including bass, to improve the sound at low volume." That wasn't the right setting for my situation. It can be turned off from the controller as follows:
1. From the Music Menu, select Settings>ZonePlayer Settings.
2. Select the zone corresponding to your S5
3. Select Music Equalization.
4. To change the Loudness setting, touch On or Off.
5. You can also individually adjust bass, treble, or balance sliders