Re: Good books for learning 'advanced guitar theory'
+1 to the above.
Modes are pretty simple though, and easy to remember. Think of them in the following order:
You can remember the order with a mnemonic - eg "I Don't Play Loud Music After Lunch".
C Ionian is the C natural major scale - eg all the white notes starting from C. Each successive mode can be remembered as all of the white notes starting one higher each time: so D Dorian is all the white notes from D, E Phygrian is all white notes from E, etc. A Aeolian is the A natural minor scale. Modes with different root notes just involve transpositions of the same interval patterns: so D Ionian is D E F# G A B C#, and so on.
Learning the modes for guitar is easy, but takes practice to remember them. Do that, though, and it's a good jumping off mode into more complex theory.