Complex sentence: Morrison had intended to record the album "a cappella" (with only vocal backing) by a vocal group he called the Street Choir, but the five songs released on the album that included the choir also featured a backing band.
Split into simpler sentences: Morrison had intended to record the album "a cappella" (with only vocal backing) by a vocal group he called the Street Choir. However the five songs released on the album that included the choir also featured a backing band.