I've literally tried every method with Symphony II (6 DISC) and also Concert radio, at first i got myself connects 2 Aux to FM which basically works on every car, it connects in between your radio and your radio antenna and allows aux input via the fm but quality was pretty amazing. However just recently managed to pick up a Dension BT Lite for £40 new on eBay (these are well over £100) but has USB, Aux and bluetooth.
If your looking for cheaper alternatives its either Connects 2 or Yatour... both have USB + Aux.