I don’t have a DCS51 but looking at the photo on the Digitrax page it almost looks like the back of the case can be unscrewed leaving the front panel and about 3/4" of the case?
Digitrax uses off-the-shelf housings for most of their equipment.
Could you remove the front panel, cut a hole into your panel slightly smaller than the outside case dimension and sandwich it into your panel?
Using the back half to cover the electronics? You would probably have to use longer screws.
Or make up aluminum angles to make a flange bracket that can screw to the sides of the housing (I would still open the case and use short machine screws) and you can flush mount the panel from the back, through an opening in your panel.