Not sure if you have this sorted but for anybody who needs to mute just there laptop/pc speakers and just let the sound work on there device media player avr reciver ect
on win 7 not sure about win8 as do not use it
step 1 right click your speaker icon and click on volume control options
step 2 in the box make sure you tick your default speaker click apply
step 3 just click the speaker icon and you will notice it only shows the level of your speaker no other device just cick the mute button and the music will be muted on the pc but will continuse to play on your dlna device.