Early on in the digital sound days, many theaters did have multiple digital formats because each studio was supporting either one or some but not the other. Eventually, many studios started supporting the QUAD format: Dolby Digital (plus Dolby SR optical), DTS, and SDDS on one print. Why they didn't do this earlier is beyond me, and to this day some prints still do not do this. DTS would start out as the dominant format because it was much cheaper to implement, but eventually, Dolby surpassed it. AMC Theatres for awhile only supported SDDS, which was an absolutely terrible move considering the equipment reliability and the fact that it was the format that had the least amount of market share. Many argue, however, when it did work, it was in fact the best sounding format available. Seeing Titanic in SDDS is definitely an experience I've never forgotten.