Roland MC-09 overdrive upgrade

MC-09 sounds great (i know ,not like a real one) but in the DSP 303 simulation they forgot some effects : the OVERDRIVE (which is not on the original 303)

It's possible to add a overdrive plugged on output but not funny enought. I want to add a overdrive inside the box with a Jack plug output.
Connecting  the overdrive on the RCA output (but internaly) will not allow to get the overdrive on the headphone plug.

for my point of view it's better to add overdrive after the DAC,  (and before the volume button)so you will get the overdrive on each output (and headphone) but without a  schematic i need to search inside the box.
I saw that the MC-909 got several similarities in the IC used(especially the dac and op amp), and the MC-909 service manual can be found on the net. Will investigate this way.

Update :
I've found where to connect this  please the pictures :

 Here is a quick schematics on how it is organized , i plan to add the Overdrive on the red trace.

The different opamps and the pint where you should find audio. (white and red)

The different opamps and the pint where you should find audio. (white and red.
the point marked  1 are after the volume amp.
the point marked 2 are after the headphone amp.
the point marked 3 are before the volume pot, we should replace the 2 caps by the overdrive.