Use surround sound, either natively or through software (Razer Surround works fine).
Enabling Loudness Equalization under Enhancements in Speaker Properties alleviates this issue for users without headsets or users streaming through Steam Link.
The thread at Steam Guides explains how it works and has a download link.
The Dark Arisen expansion removed the awesome original theme song and replaced it with a new one. You can bring back the original song by simply downloading this mod with the Nexus mod manage or following the steps on the reddit thread below: