With a fresh installation of Max2Play, you should immediately get the option to select HiFiBerry, HB DAC+ and your player setup in our web interface. The dropdown menu for output device selection should definitely give you options that include „hifiberry“ in the name, these output devices all work with the sound card. Our default and recommended one is „sysdefault…“.
This is literally what is selected, when you saved your DAC+ as the sound card in use and rebooted.
We will consider adding a test button for a quick audio check, thanks for the input.