Definitely not an expert on this, but you would need MIDI in/out cables with a USB converter. However, first you'd need to check if your keyboard supports MIDI in/out (I'm guessing probably not, though). Check your keyboard's manual if you have one (or the back panel of your keyboard).

It definitely supports midi in/out. But the playback sound I get does not seem to be the Garritan JBB3 voices I installed on my computer.  I do hear them when playing back from the internal audio devices.

I do not believe you can suck the Garritan sounds into your keyboard, if that is what you are trying to do. The Garritan sounds play through the computer's Aria player.

MIDI is not audio. Through MIDI can’t trigger sounds in your keyboard that aren’t present.

Is your keyboard capable of being an audio interface for your Mac? Can you hear other Mac audio through its speakers?

If yes, then what you want is possible and your manual or Yamaha support should be able to help you.

I can’t say that I’ve ever heard of a keyboard with this functionality. I certainly don’t know everything that’s out there.

Long time ago, in the 20th Century, I had a Yamaha keyboard with some great internal sounds, much better then the General MIDI and whatever Finale was using at the time.

To get those sounds from Finale, I had it trigger the Yamaha and other sound modules via MIDI while sending the audio out into Digital Performer on another Mac through an 8 channel MOTU interface. The 2nd Mac functioned as the Master Clock so that, when I hit Record in DP, Finale started playing. Looking back, it’s a miracle that the whole mess worked—but it did.

I don’t know if I could remember the exact setup to ever make that work again. I sure the heck do not miss those days.

MIKE,

Yes, I normally play back to my Yamaha keyboard.  It's just that the sound is very ordinary.  All the instruments sound pretty similar.  I just wanted better as is provided to the internal audio by Garritan JBB3.