@TonyW: thanks for the detailled information! I just tested with your settings (enabled DTOverlay for hifiberry dac pro) and it is working for me (BT-adapter available). Just to make sure it is not because of insufficiant power: remove all other devices (usb-drives, display, etc.) from the Raspberry (maybe also remove the hifiberry card) and check if that solves the problem with bluetooth.
@all: Bad BT-connection and playback errors (crackling sound, breaks) can be because of bad power supply and/or too many connected devices (usb-drives, display, etc.). You probably need a USB-Hub with an external power supply for USB-Drives and a strong power supply if a display is attached to your RPi. If you have your Pi in a solid metal case, this might also cause bad bluetooth signal and you may try an USB-Bluetooth dongle to improve the connection.