Use the line in jack, which is probably stereo, and lay down the tracks from your keyboard. Then you can come back and lay down the vocal track(s). Nothing to it!

Cheers,

Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!

K+E=W (Knowledge Plus Experience = Wisdom.)