Complex sentence: Lambesis received demo tapes from a band called This Endearing, of which bassist Josh Gilbert was a member; however, Lambesis chose to "sit on it" and waited for the band to record more material.
Split into simpler sentences: Lambesis received demo tapes from a band called This Endearing, of which bassist Josh Gilbert was a part. Lambesis wanted to "sit on it" and wait for the band to record more material.