[uptheoctave]

You can use HDX as a core audio device but you won't want to.

It's latency is pretty terrible and you don' get any of the low latency advantage/DSP when using it as a core audio device.

I have a HDX card plus a MTRX.
I use a Focurite Rednet card for native, sending the MTRX's inputs to the Rednet card and it works great.