The inputs can be implemented as single ended, however by implementing single ended inputs and outputs you lose some of the benefits of differential signals, especially the noise immunity offered by the differential lines. For single ended applications we suggest the unused audio input to the DS4420 is AC coupled with a capacitor between the unused IN pin and GND. If a long line, cable or trace connects the audio source to the DS4420 and the unused input is grounded closely to the DS4420, then the noise rejection could suffer and the overall output quality may degrade. Also, if all other conditions are the same as the differential case, the single-ended output will be approximately 6 dB lower (but this can easily be accounted for by the 3dB programmable gain step size).