For one, the additional I2S input capability on the digital board. One might be able to tap wires to it and connect the I2S output from a DAP. This is of course provided Audio-gd has fixed the I2S / Sabre32 clock issue.
The problems is on the ES9018 , while it accpet the I2S, it had very rigorous request the I2S signal because its I2S input pots are without the master clock input.
I asked an engineer work for another manufacturer, he said in their gears , the I2S input will change to SPDIF then feed to the ES9018.
So I don't think the ES9018 can support I2S input as well.
But we have find the way to fix this problems.
The ES9018 must need the input master clock and built in a master clock selector can automatically choice between the I2S master clock and the 80MHz main clock.
Would the use of the M2Tech usb/rca key avoid that problem or it has nothing to do ???? (Maybe I misunderstand this....)