Tomaso it might be a pointless exercise. Usb audio is bit perfect pass through but with no navigation / phone audio (which leads me to think it's taken before the AKM DSP). Taking i2s from this point wouldn't have any advantage over usb audio.
Looking at the AKM DSP datasheet looks like audio from navi or phone is going via DSP2 on the AKM (chip it has actually 3 DSPs) and mixed together. (here is spdif taken from). Taking i2s from this point doesn't offer any advantage over spdif.
So, it would seem like having a diy with i2s would be just a waste of time as the Dudu7 already provides output from before dsp (usb audio) and after dsp (spdif).
If you consider AKM dsp has over 100dB S/N etc etc, what would be the point to go to a purer signal? Your amps in the car merely reach usually 74 - 90dB S/N (not weighted), plus driving a car pretty much adds such a noise that probably hearing 70dB and 100dB dynamic range is the same.
All other things, like THD or frequency response on spdif with Dudu are excellent (albeit slightly worse than on usb audio). Except the level which is capped at 0.9.
So, question remains. Why?
