Correction; the Amiga has audio ports on pin 11 and 18, and have (-)12 voltage levels on pin 9 and 10. Pins 11 and 18 are apparently not according to the RS232 standard. But I don't think any of these pins will be put on the db9. Many signal lines are not necessary, rxd (receive) and txd (transmit) and ground are the only essential pins (USB for instance has only these signals).