Bill,
No problem. Fire your vocal mic through the keyboard's mic/line in. Fire the keyboard's output via the RCA connectors through the mixer's tape in. Now you have all the other channels free for other instrments and mics. The mixer's stereo output is then fired directly into the Z-2200's input. All the volumes will be controlled with the mixer.
Good Luck,
Gary
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Travlin' Easy
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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.)