Sounds like some progress at least.

The RichAuto website download page is here: Download Beijing RichAuto S&T Co. Ltd

Ensure the file is downloaded as a binary file (depends on how you downloaded it).

Another option might be to load the image into the DSP's "inner" memory and try from there.

1. Leave the CNC machine off and remove the USB stick from the DSP
2. Connect the DSP to the PC using the "flash drive mode" (hold down two buttons and connect USB cable)
3. From the PC, copy the firmware to the DSP handle (they call the DSP internal storage "inner memory").
4. Try the Emergency upgrade and use the image in the DSP.

If that doesn't work, try contacting RichAuto directly. They have a FaceBook page to which they do respond but not very quickly from what I've noticed.

Here is a copy of the A15 firmware (from the above). It is not a ZIP file so just rename (remove) the ".zip" from the filename (I added it to allow it to upload here).

Good luck!