You need a way to get your Mac audio output to your keyboard amp. You computer controls the audio (that's why you hear it through the computer speaker), but the MIDI data is going out the computer to the Ketron, and then it is sending its audio out (the sounds it generates) to your keyboard amp.

Another option is to run the Ketron output back into the computer (assuming you have some line-in capability), and then run the computer output to the amp (which will mix the audio and midi sounds together).

I'm not a Mac guy, but it may be as simple as connecting your headphone jack into the amp (possible through a mixer, although my keyboard amp has multiple inputs, so I can have more than one device plugged in). However, I generally connect a small Behringer mixer to my amp, then run my audio devices (my computer, possibly an iPod, or any other audio device) to the mixer. My Casio keyboard then gets connected directly to the amp, and the sounds get mixed from the keyboard at the amp and everything sounds great.

Don't know if that helps or not.

John

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