A low-power 20kHz signal on a PCB track not designed to radiate is not going to be a problem at all - plus you can always switch to terminating with a resistor

A low-power 20kHz signal on a PCB track not designed to radiate is not going to be a problem at all - plus you can always switch to terminating with a resistor in the unlikely case it is a problem. Also the author mentions connecting directly to the DAC, most DACs, and definitely all DACs I have studied the datasheet for have a CE (Chip Enable) signal, or some more advanced way to control audio output with a command (using an SPI or similar interface), no need to cut the audio connections. Reality isn't as simple as applying basic physical knowledge without the required context.