Hi Tim,

just had a look and a try to your site.
The player behavior is not related to responsivizer, that manage only the layout.

Looking at the player, i see that it comes from a component 'com_quicksell' and it seems Flash based. If so probably this is the problem, most mobile devices supports HTML5 player but no more Flash, especially Apple devices.
In this case the only solution would be update the player to an HTML5 one, supported by all mobile devices.

PS: on my Android i was able to use your mp3 player.

Cheers,
John