Hello people! I play at a church, where two keyboards are connected to the PA system through DI Boxes. I recently bought a macbook pro, connected a keyboard to it via midi, unplugged one of the 1/4 inch cable connected to the keyboard, plugged a Y-cable in the headphone jack of MBP, and connected the 1/4 inch cable there. I tried playing thru the PA, but the volume was too low thru the system... Also, the sounds came out all distorted... Do I need an external sound card to work this out? What am I doing wrong?!