interesting.
I have a DAS, and F12 just works (MacPro), option or ctrl (i forget) +F12 will eject the second optical drive if you have one.

not sure if there are volume equivalents though. I'll have to try this when I get home.

I also use a Cherry switcher keyboard after my G5 keyboard is retired, and I found a perfect way to remap the keys.

I modify private.xml instead of checkbox.xml, the benefit is I can also enable "Don't remap Apple's keyboards" and "Don't remap Apple's pointing devices" that provided by checkbox.xml.

I remap PC_Application key as Eject, and remap PC_PrintScreen/PC_ScrollLock/PC_Pause as Volume_Down/Volume_Up/Mute.

I use PC_Application as Eject, so that I can easier press WIN_R+ALT_R+APP to let my MAC sleep, because all these 3 keys are together.

Here is my code:
~/Library/Application\ Support/KeyRemap4MacBook/private.xml


<?xml version="1.0"?>
<root>
<list>
<item>
<name>Volume and Eject Keys</name>
<appendix>Up, Down, Mute, Eject</appendix>
<identifier>remap.volumeKeys</identifier>
<autogen>--KeyToConsumer-- KeyCode::PC_PRINTSCREEN, ConsumerKeyCode::VOLUME_DOWN</autogen>
<autogen>--KeyToConsumer-- KeyCode::PC_SCROLLLOCK, ConsumerKeyCode::VOLUME_UP</autogen>
<autogen>--KeyToConsumer-- KeyCode::PC_PAUSE, ConsumerKeyCode::VOLUME_MUTE</autogen>
<autogen>--KeyToConsumer-- KeyCode::PC_APPLICATION, ConsumerKeyCode::EJECT</autogen>
</item>
</list>
</root>