While there are chord symbols & Roman numerals used to name a Neapolitan 6th chord, I haven't come across either of these for naming an Augmented 6th chord. The only names written were Italian 6th, French 6th and German 6th. The symbol for each was It.6, Fr.6 and Ger.6. Is this the only way to represent this chord?
Also, while using the Augmented 6th chord in a chord progression, I read that this chord is generally followed by chord V, or it goes to chord Ic and follows the cadential 6-4 progression i.e.
ic - V - i. Are these the only possible ways of using the Augmented 6th chord, or there are others?