Thing is, as far as I can tell, the Fall of the various archons, was masterminded by Lucifer- who, as the Avatar of the Overlord of Hell, was always evil.
In 3.5E, only the Pact Primeval version in FC2 stresses Asmodeus began as a nonevil guy.
That said, 4E has it's own approach- which does involve the guy we now call Asmodeus being corrupted by an "older" and even more evil entity (CE rather than LE though). This is recounted in Demonomicon.
The corruptor of Asmodeus is (spoilered):
SpoilerPazuzu.
Using Dicefreaks as a starting point, does make the most of the existing material. And there's always room to modify it to be more WOTC-like, if you want to run a game with Dicefreaks-level power, but WOTC-style history.