I'm using a Raspberry Pi 2 with a Hifiberry DAC+ Pro and the Adafruit 3.5" touchscreen.
I attached the DAC+ to the Pi, and then the touchscreen to the DAC after soldering some extra connectors. It works fine until I actually try to play audio, the touchscreen shuts off and I'm not sure how to get it to turn back on (the sound plays though). It seems either the display will run or the sound, not both.
I installed Raspbian with the HifiBerry Installer and got the touchscreen to work by following the Adafruit website's guide
I've tried looking at the lightdm log and tail but nothing obvious is coming up.
UPDATE: It looks like the problem was with GPIO pin 18. It seems both the DAC and the touchscreen use it, using this reference helped me fix it.