.......... to know what the Digital Out is for. And what is the 5.1 DTS support?
the digital out is for an optical cable. Your digital audio signal travels through this. If you want Dolby Digital or DTS you must have this cable. It supports DD5.1 meaning if a movie has 5.1 or DTS 5.1 and you have your PS2 connected to an AV Receiver that will decode the signal and you have the speaker set up, you can get the 5.1 reproduction.