Modifying AppleUSBAudio.kext

Hi,

I'm not a dev, but this seems like the appropriate section of the forums.

I have a Fiio E7 USB DAC. When attached to either of my Macs, it's detected successfully as a "USB Audio DAC". This Fiio device ignores the current system audio volume setting, similar to when outputing audio over the optical port.

When I select the optical digital out port in SysPrefs, it automatically greys out the menu bar volume icon, greys out the volume control in SysPrefs and, should you use the keyboard volume keys, causes a "volume disabled" graphic to be displayed. This behaviour is not replecated when the USB Audio DAC option is selected, even though it functions comparably.

I've found what I believe to be the kext responsible - AppleUSBAudio.kext - for governing OS behaviour when USB Audio devices are attached. How would I go about modifying it to:

1) replicate the behaviours employed when using the optical audio port

2) replicate the above behaviours on a per-device basis?

S.