I don't think you can do this directly over the HD500/DAW usb interface. In order to reamp using the HD500 you need to have the incoming signal routed through one of the HD500 Inputs (Guitar, Aux, ...). The incoming USB signal does not get routed to the DSP.

So that means you could try using your Fireface as the intermediary. I haven't done this, so please understand that this is just a theoretical suggestion - but it might be worth trying.

Configure your DAW to use Fireface as its audio input and output device. Route the dry track from your DAW through the Fireface audio output into an appropriate input on the HD500, The Guitar and Aux inputs are instrument level; the FX Return input can be configured as line level. Select your HD500 Inputs accordingly (or place the FX Loop at the front of the chain; you may have to use a dummy jack in the FX Send to enable the loop) and set up your patch processing. Then route the HD500 Output (use Studio mode) back to your Fireface audio input for recording the processed signal in your DAW.

Again, just theoretical......