Complex sentence: Lukather, who had been a self-taught musician until then, began taking guitar lessons from a musician named Jimmy Wyble, who expanded Lukather's knowledge of different aspects of music, such as orchestration.
Split into simpler sentences: Lukather, who had been a self-taught musician until then, began taking guitar lessons from Jimmy Wyble. Wyble expanded Lukather's knowledge of wider aspects of music, such as orchestration.