I would like to suggest to make available an option to make the background color of the audio player transparent.
Right now the player has a default white background, and it can be changed by the shortcode inline parameter bgcolor, but it only accepts opaque colors, and the flash paramtere wmode is also set to opaque.
My suggestion is to make the default behavior for the player to be transparent, by setting wmode transparent, unless there is an explicite bgcolor set, then set it to opaque.
Lines to modify for a quick fix:
128 $bgcolor = '';
254 <param name='wmode' value='$wmode' />
And add a line before in around 246:
$wmode = $bgcolor ? "opaque" : "transparent";
Hope to see this in a future version!