Hi, as I said in the reply to the post you linked:
Number one, that should not be necessary. That card should follow the exact same procedure as the others I.e put output = hifiberry_dacplus in settings.ini. If any other steps are required then that is a bug.
The steps described in that post are not how musicbox v0.6 is designed to work. I suggest you restore /boot/config.txt to exactly how it was and set output = hifiberry_dacplus in /boot/config/settings.ini. Then if you can post the exact error message you get we can go from there.
If the output works, but is distorted or too loud then please follow the good advice at Settings for piMusicBox 0.6 and HifiBerry Dac +? - #7 by jcass77