For Rank 6 Music Knowledge you have to acquire The Soundbox: Heart of the Instrument. The wiki says you can obtain it from fishing at Port Cobb or doing Barri Advance for Three, but I thought I could fish it up and have not seen it drop once(Done around 50 hours of fishing, oh glorious grinding ). Anyone know if its still possible or if I need a certain rank for fishing(Rank 9 Currently)? I appreciate any help!