thanks for the bug report! i'll have to try and track this music issue down the next time i work on the web browser port of my engine's audio backend.
i've been meaning to add an exponential/logarithmic curve to the game's volume controls for a while, but i was worried it would take a lot of work. after giving it a quick try, it all worked after just a couple of minutes! so the next release will have more fine control at lower volume levels.