I'm able to do everything except play/pause by controlling the 4 circuits I described.
Sending 100mS pulses through a 1K resistor into circuit D turns the volume up.
Sending the same pulses into circuit A turns the volume down.
Pulling circuit A low for 100mS goes to the previous track.
Pulling circuit D low for 100mS goes to the next track.
So far I have not wrecked the chip, but if you play with this be careful about driving the lines with the Arduino, hence the 1K resistor when pulsing lines high.