There are only two audio outputs on a PS2. Component and phiber. Since only tv's have component, you will need a phiber system to play sound. There are two options:
A: Get a SoundBlaster Sound card. These come standard (I believe) with phiber input/output jacks.
B: Get a surround sound system (A GOOD ONE!) I got mine from BJ's for about $1k, and it comes with a Kenwood audio reciever -w- two phiber inputs, a Kenwood DVD player (really nice BTW), and a 5.1 Bose surround sound system with a HUGE subwoofer. Only one problem: the police came to my house, and I'm not allowed to play MOH after 9PM anymore...