Selecting this as recording device in Audacity should let you record all the channels at once automatically.

Some audio interfaces however will display a 'Multi' device. This may mean having to delete silent tracks after recording. You may need to increase the number of recording channels in Audacity preferences (possibly to the maximum supported by the device, even though you are only recording a subset of them), until all you want are included. Channel selection: You cannot select exactly which channels are used - Audacity will simply use the first ones it finds.The number of channels desired can be selected in the Audio Settings tab of Preferences. Audacity supports recording however many channels the device offers (for example, 24). Application support: the application you are recording into must support working with multiple channels of audio.Also, consumer-level systems are not designed to achieve the low latencies and high throughputs needed for high quality multi-channel recordings. This is more problematic that it might seem because the standard sound interfaces for many operating systems were designed long before multi-channel recording was possible, and so only allow for up to two channels of recording. Driver support: the drivers for the device must make it possible to record more than two channels at once.You will need at least a semi-professional device to find support for multi-channel recording.

Most consumer cards only have one stereo pair of ADC's that is switched between various inputs such as Line-In and 'Mic'. Hardware support: you need a sound card or external audio interdace which has enough Analog to Digital Converters (ADC's) to do multi-channel recording.

Rodecaster pro audacity