The AM Forum

A source of technically sound information regarding audio equipment and how to properly interconnect it, is available for download free of charge. Check out "RaneNotes" at the following website:
http://www.rane.com/library.html

They have a wealth of technical data on balanced vs unbalanced lines, interconnecting balanced and unbalanced inputs and outputs, mixing together balanced and unbalanced audio equipment, preventing and dealing with ground loops, rfi problems in audio equipment, Pin 1 problem and much more.

Here is an index of their entire library of RaneNotes by number and subject. Click on the link for an HTML version for the note.  At the bottom of the last page of each note is a link to a PDF version.  I find the PDF version more attractive and easier to read.  
http://www.rane.com/library.html#gpm1_2

I would particularly recommend downloading and printing out the following:

Note 151: http://www.rane.com/pdf/ranenotes/Grounding_&_Shielding_of_Audio_Devices.pdf

Note 110: http://www.rane.com/pdf/ranenotes/Sound_System_Interconnection.pdf

Note 165: http://www.rane.com/pdf/ranenotes/Pin_1_Revisited.pdf

Note 166: Rfi and shielded balanced lines (http://www.rane.com/pdf/ranenotes/SCIN_Shield_Current_Induced_Noise.pdf)

I am considering downloading and printing the entire library on front/back sheets, and taking the whole thing to some place like Kinko's and having them bind them into a permanent booklet.