Posting to confirm that I have done this mod to my A4 as well and its great. I've had no issues so far and its really opened up the synth for me and my computer-less set-up.
I concur that you should open up the synth ahead of time and ensure the jacks you are picking up fit correctly in the synth. Its tight but definitely doable. I can't seem to find my order for the ones I used but if I stumble upon it I'll post it.
Edit: One "issue" is if you mute the voice from the main output via settings, it is also muted from the individual output. But since the individual outputs are stereo, I have my main output panned left and all the individuals panned right so my main output is the remaining tracks. Its ok by since I only run mono into my octatrack, but yea not great.