help understanding architecture of audio

[don fisher <dfisher as arizona edu>]

I am quite familiar with connecting arbitrarily complex audio systems. I 
have been trying to understand how the sections of the linux audio plug 
together.

For sources I have a microphone, audio and video CDs, and MP3s. For 
output I have an audio jack, a bluetooth transmitter.

Is there a mux (or preamp equivalent) that allows one to select and 
input and output path? Perhaps also set the gain, balance, base, treble 
and loudness.

Is there a document that describes haw to turn on, and then access the 
various input and and output channels.

Sorry if this is to basic a question. All of my searches have found 
pieces, but I am confident there must be an top down design document.

don