Complex sentence: Pedro Aznar was a lesser known bassist who had once been a member of progressive rock group ALAS, but he also happened to be a friend of Moro's who knew of Aznar's ability with the funk and jazz base.
Split into simpler sentences: Pedro Aznar was a lesser known bassist who had once been a member of progressive rock group "ALAS". He also happened to be a friend of Moro's, who knew of Aznar's ability with the funk and jazz base.