What DCS unit? A TIU has 4 channels. Yes, a DCS explorer only has 1 channel.
The book being referred to is the DCS companion. https://mthtrains.com/DCS_Companion
Depending on what exact DCS control system you have the rules are different.
TIU- again 4 channels, 2 are fixed voltage meaning the TIU does not modify the incoming voltage to the output, and then the 2 other channels are variable- meaning the TIU can modify (reduce) the voltage compared to the input or just pass through "fixed". As long as you power the logic of the TIU, the voltage inputs can be variable from a transformer meaning you can turn them on and off and vary them and the TIU stays running. Another factor at play, this can be used in passive mode, where it only is used to provide the DCS signal to the track out of each channel and is not passing any power.
The DCS explorer WIFI box unfortunately has many more limitations. It MUST have at least 12V constant power source or higher. This is because it takes time to boot up the wifi and so forth and uses the incoming power to power itself and only has one input. Thus it's near impossible to use it on a conventional track because you need constant power coming in and it does not provide a "variable" channel output. This cannot be used in passive mode.
The DCS IR commander can also be run in passive, but is extremely limited in function and also not the strongest signal output.
