Zuki,
If you use two powered monitors, you will still be able to run your keyboard in stereo...I use an old pair of Yamaha MS60 powered monitors (don't need a sub with them)...work fine for my jobs, but in your case, you may need more power.
The Mackies are great.
Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.