Frisby surround system won't work on my TV.?

I bought a Frisby surround system. My tv has an optical output and my surround sound is RCA. So I bought a optical to RCA adapter and plugged it into my tv and surround sound. I can hear the sound but it's really faint and static. I've spent so much money and many frustrated hours trying to get this thing to work. Anyone have any ideas? I need help