Complex sentence: By this time, Sulzer had become the group's manager, while the duo continued to record demos with Osborn, one of which was sent to A&M Records via a friend of Sulzer's.
Split into simpler sentences: By this time, Sulzer had become the group's manager, while the duo continued to record demos with Osborn. One of these demos was sent to A&M Records via a friend of Sulzer's.