Gnome keyboard configuration for multi channel sound card.

Hi, I am trying to configure the volume keys of my keyboard to control volume on Maudio 7.1 sound card. In gnome desktop preferences --> Key board shortcuts, I've set up volume up and down as XF86AudioLowerVolume and XF86AudioRaiseVolume respectively. Similarly, mute button as XF86AudioRaiseMute. Problem is that these keys only work for one channel (right speaker). I would like to setup 2 channels (Right and Left) to be controlled by these keys. Where would I make appropriate configurations? Thank you! SB.