Passthrough video but not audio

I have a problem with audio in this specific situation. I have a Sony Dav-DZ500F home theater  system. It has very limited input connection options. (no HDMI, no optical). My tv is an old CRT tv with only 2 scart and one composite input. My only way to connect my TV LIVE is composite. Video ■■■■■, audio ■■■■■ big time. The sony unit has 3 RCA inputs (composite like, red-whte-yellow), and calls it SAT input. The manual says that i can connect there an external player and the sound will come from the 5.1 speaker system. I have tried this with my TV LIVE and i had video but not audio. I think that many folks in this forum know way better than me in this field. Any help please?