In the beginning of Book 9 Where Augustine says "But where through so many years was my freedom of will?" I think he basically says conversion is being given a new will, a truly freed will. I think his bit of rhetoric in asking the question is to say "I had no free will, but received a freed will." But Augustine, I believe would shy away from saying it was "compulsed," he often says compulsion is negative, but maybe would say he is drawn: pulled, not pushed.
Piper has a quote from one of Augustine's letters where Augustine states: "Who has it in his power to have such a motive present to his mind that his will shall be influenced to believe?...If those things delight us which serve our advancement towards God, that is due not to our own whim or industry or meritorious works, but to the inspiration of God and to the grace which he bestows." So I guess then Augustine is very Edwardsian or more properly, Jonathan Edwards is very Augustinian. A will is free to pursue that which it delights most in, but not to chose what it delights most in.