Equinox produced Styx's first single with A&M, the highly spirited "Lorelei," which found its way to number 27 on the charts. Although it was the only song to chart from Equinox, the album itself is a benchmark in the band's career since it includes an instrumental nature reminiscent of their early progressive years, yet hints toward a more commercial-sounding future in its lyrics. "Light Up" is a brilliant display of keyboard bubbliness, with De Young's vocals in full bloom, while "Lonely Child" and "Suite Madame Blue" show tighter songwriting and a slight drift toward radio amicability. Still harboring their synthesizer-led dramatics alongside Dennis De Young's exaggerated vocal approach, the material on Equinox was a firm precursor of what was to come . After Equinox, guitarist John Curulewski parted ways with the band, replaced by Tommy Shaw, who debuted on 1976's Crystal Ball album.