M20/M40 - FAQ - Can I use an external DAC connected to the analogue input?
The analog input is converted to digital using a PCM chip. Using a DAC with its higher-grade audio coverters won’t improve the M20/40 input. In another words, when the source is connected to the DAC, it may get digitized at a higher resolution, but when it is transferred to the M20/40, it will be digitized again at a different resolution. A much better result can be achieved by connecting the DAC to the M20/40 via the optical input, as this will provide full 24/192.