The input / output channel numbers of adc~ and dac~ currently map directly to audio device channel numbers. It would be useful if there was an application-wide way to create a mapping between adc/dac channel numbers and audio device channel numbers.
In Max, this is achieved via a per-channel mapping (see attached screenshot). However, a simpler approach would be to allow a "DAC channel offset" and "ADC channel offset" to be specified in the Pd audio preferences dialog.
With a DAC channel offset of 0, then dac~ channel 1 would be mapped to audio device output channel 1. With a DAC channel offset of 8, then dac~ channel 1 would be mapped to audio device output channel 9.