I've had my DM9 with 32GB Runcore running 10.5.8/EFI 1.2a PERFECTLY for months now. This is my FIRST issue and I'm not sure what caused it but the fix was easy.
My DM9's sound stopped working out of the blue. We just opened it and there was no longer any sound. It did not happen while someone was using it so I can't figure out what happened. I tried rebooting and still no sound. Also the sound icon was no longer in the menu bar, as I had checked the box for it to be so.
I went into the System Preferences/Sound/Output tab and the sound slider's Mute box was checked and grayed out so I couldn't un-mute it. The box WAS checked for displaying sound in the menu bar, but it was still NOT there. I unchecked and check this box and could see an "invisible" icon space in the menu opening and closing between the other icons (weird).
THE FIX: I rebooted the DM9 to make sure everything was closed and running in default. I ran DellEFI 1.2a5 and clicked the Custom Installation button, unchecked everything but the "Reinstall Dell Mini 9 Extension" box. Pick ONLY that one and click Install. After the reboot everything was back to normal.
Hope this helps others.