I'm considering connecting my hifiberry to the existing 3.5mm jack of the RPi main board. I would accomplish this by removing the DC blockers (C34 and C48) from the rpi board and connecting the hifiberry L/R signals to these points.
My question: are the analog grounds the same on the hifiberry and the rpi audio outputs? The analog ground can not be easily disconnected from the jack.
Hijacking the RPi jack