Панорамирование HTML5 Audio
Вот, что удалось найти, надеюсь поможет: 
Audio Stereo Panning
HTML5 Audio currently has no way of panning audio tracks left or right (adjusting the balance). Recommend adding a HTMLMediaElement.balance property, floating point decimal, with a range of "-1" (full left speaker), to «0.0» (center, both channels at full volume), to «1.0» (full right speaker). This should work on both mono and stereo tracks.
var sound = new Audio('env/water-loop.mp3');
sound.balance = -1; // full left speaker
sound.play();

Changing this value should have an immediate effect on audio that is already playing — i.e. balance should not be buffered.
А если сделать два одинаковых трека, один только с левым каналом, второй с правым, и управлять их громкостями?