Complex sentence: He is more proactive as a member of Rehasher--as their lead singer, guitarist, songwriter, lyricist, and producer; although Manganelli only works with Rehasher when Less than Jake has time off.
Split into simpler sentences: He is more proactive as a member of Rehasher--as their lead singer, lead guitarist, songwriter, lyricist, and producer. Unfortunately, Manganelli is only able to work with Rehasher when Less than Jake has time off.