If there where one setting that worked best for all then they would be fixed and not adjustable.
With my TRX-2 the DSP level does nothing for DMR, it's probably only for p25.
ADC is the signal level into the decode chip and again no difference noted in DMR bit error rate. P25 setting?
DAC are the audio level out of the chip and can be adjusted so that analog and digital sounds equally loud and doesn't influence the decode performance.