Complex sentence: The Rivals the group went onto record their debut music video in addition to a large stint of publicity which left the band exhausted with band manager John McMahon continually pressuring them to promote single "Sound of the Underground".
Split into simpler sentences: The Rivals, the group went onto record their debut music video. In addition to that, a large stint of publicity left the band exhausted, since band manager, John McMahon, continually pressured them to promote the single "Sound of the Underground".