Russ Solomon was the driving force behind a sprawling enterprise that began with one store in 1960 and grew into a dominant competitor in music retailing. Sales of recorded music, videos and books eventually topped $1 billion a year. With marketing instincts that even rivals and critics called ingenious, he built megastores, some bigger than football fields, and stocked them with as many as 125,000 titles, virtually all of the popular and classical recordings on the market.