They apply to anything digital, so both DMR and P25.
DSP has to do with some threshold that the digital signal processor utilizes. I'm a little vague on the specifics. Some report that modifying it can improve performance on simulcast sites, for instance. There was a thread recently to post DSP values that people like, but I'm not sure it caught steam. I haven't noticed any huge breakthroughs playing with the setting, but I have not tried playing with it since the DMR firmware.
ADC is the analog to digital converter gain. This is the most import of the three settings. It allows you to adjust how "hot" the audio is that the DSP receives. Generally, you want to be 0 or below. I am not aware of any instance where someone was helped with a positive value.
DAC is the digital to analog converter after the signal processor. It converts the digital audio back to an analog signal that can drive the speaker. Essentially, it is a global "auto gain control" for digital audio vs. analog audio. Modify this if digital calls are louder/softer than analog calls across the board. There are also several other settings to account for this problem.