A few useful links.
Interactive Frequency Chart
Delay Time Chart
What is dither?
Mastering Guide (by Izotope)
Mix Headroom Guide
Setting up a nearfield monitoring environment
Intro to Mid/Side Processing
We have a Recording and Engineering group, a Mastering group, and groups dedicated to various DAWs, but no group that's focused on the mixing itself.
Recording and Engineering tends to focus more on the technical side of things, what hardware is great, which computer system is best, definitions of things like line level, how to record various instruments and the like.
The Mastering group focuses on the art of mastering a mixdown.
This group is where you could post a link to a mix, and have a dispassionate discussion about the mix, get constructive criticism, get suggestions on how to address things in different ways, ask questions about how to solve a problem, and a place where you could learn more about the art in between the recording, and the mastering.
A place to share tips, techniques and "secrets" that you've learned or read about with the goal being that anyone who is interested can learn and improve their own mixes on projects, and where people can explain how they did something so other's can learn.
This is also a group where there will be overlap with the mastering and DAW groups by the very nature of the tools used for mixing and the end result the mix is aimed for.