Hello, I need to record my keyboard sound into garage band. It is a Yamaha Portable Grand DGX-505. It has a micro usb port, a 1/4" output jack. I tried to get a mono 1/4"- split 1/4" audio cable. The cable was a "grounding cable". It didn't work. What do I need and how do I set it up in GB? I would like the sound to be the sound that I am hearing in my headphone. Is this possible? Thank you!!