William Layos, who served as president of Cinesound from 1988-94, died Dec. 23 of a heart attack in Los Angeles. He was 55.He worked at Cinesound, a post-production sound house in Hollywood founded by his father in 1942, for 28 years. Born in Los Angeles, he attended Northern Arizona U. and served four years in the U.S. Air Force. Layos is survived by his wife, Dorothy, a daughter, four grandchildren and a sister. In lieu of flowers, family suggests donations to Regional Organ Procurement Agency, 10820 Wilshire Blvd., Los Angeles, CA 90024.