Actually, you can do this, but not throught he USB. You'll have to employ a small mixer, plug the mixer into the LINE-IN/MIC jack and set the switch to LINE-IN. Now you can plug both your mic and laptop output directly into the mixer and fire it through the keyboard. Keep in mind, however, that the LINE-IN/MIC input is MONO--NOT STEREO. The PSR-3000 and Tyros has an auxilary stereo input in addition to the line-in/mic input.
Good Luck,
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.)