This is where most of the sound tweaking happens. The top half covers the playback settings of the 18 Kitpieces (pitch, envelopes etc). The bottom half takes care of the audio processing (EQ, compressors etc).
Note that due to how drums are usually recorded, there is not a 1:1 relation between Kitpieces and Mixer channels. Example: Cymbals are not recorded with close mics, so they have no corresponding mixer channels - they show up only in the Overhead and Room mics. Luckily (unlike in a real drum recording) you can still adjust them individually in the Kitpiece Controls section.
Here are a few notes on how the controls in the EDIT page works:
Use [Shift] to increase control resolution - If you hold [Shift] on your computer keyboard while editing a control, you get a finer control resolution, enabling high precision adjustments.
Reset a control to its default position - To reset a control to its default value, use [Ctrl]+click (Windows) or [option]+click (macOS)
Scroll wheel support - Addictive Drums 2 supports scroll wheel editing for most controls, just place the cursor over the control and use the scroll wheel to adjust it.
Instant on - To activate a “darkened” (turned off) section, just alter one of the controls and it will become active.