Ahhhh, okay. I've worked with a lot of hardware, but sound cards are the one thing I haven't messed with in driver terms. It makes sense now why the interrupt wasn't firing - it doesn't have to. So it does indeed appear to be in the getDMAEngineHardwarePointer function. I just don't understand why the hardware pointer doesn't appear to be incrementing. I'll keep poking around the Linux source and let you guys know if there's anything of import that we missed.
I've never dealt with sound either. I had written firmware for Motorola HC16 microcontroller and the SHARC DSP.
Maybe it is firing and needs to be serviced as far as the hardware goes. But OSX doesn't expect anything.
But even if you enable all interrupts, they still don't seem to ever receive any.