Complex sentence: He switched to Yamaha Drums around 1984 prior to the departure of singer/bassist Peter Cetera, but in 1988, he switched to Drum Workshop, whom he has been with ever since.
Split into simpler sentences: He switched to Yamaha Drums around 1984 prior to the departure of singer and bassist Peter Cetera. In 1988, he switched to Drum Workshop, which he has been with ever since.