I have been running the Pi 2 and DAC+ in a custom case with a Western Digital HDD for about two weeks now, with a 2A 5.25V power supply, so far without any issues. Can't say it is a defintive and exhaustive test, but so far so good.
The case is adapted from an existing design, for the HDD on one layer, and the Pi on a separate layer. The Pi layer has some room for extra circuitry and components like switches or a small display, and the case is expandable from 1 to 3 layers.
The acrylic parts are laser cut, but a few pieces of plexiglass and a good hand with a drill would serve as well. Threaded spacers, fasteners, and washers are available from a hardware store or online.
At the top of the pic, the plastic parts as they come from the shop, with protective paper on both sides. At the bottom of the pic, the HDD and the Pi assembled on the plastic parts (protective paper removed), top cover on the right:
Bottom layer, with the HDD, short spacers and long screws:
Second layer assembled on top of the first, with Raspberry pi, hat DAC, and long spacers, and checking fit with the RCA audio cables and HDD USB cable:
Cover assembled on top of the second layer using the short screws:
Another pic without a hat DAC, and different hardware:
The case works on the same principle as an erector set. The geometry can be changed using the same hardware in different combinations. The layers are square, and can be rotated 90 degrees relative to each other to change the location of the edge connectors. The height of each layer is adjustable using different spacers and screws.