I go from the left and right outputs of the keyboard into two separate channels on the mixer. Then from the left and right main outputs of the mixer to the two speakers. Left to one speaker, right to the other. No need to pan.
I generally leave the speaker e.q. and volumes set the same all the time. Volume levels can be controlled by the keyboard and/or the mixer.
On some occasions, I just run directly out from the keyboard left and right into the two speakers, not using a mixer. I would always do this except a need the mixer for guest mics, MP3 play on breaks, recording outputs, etc.
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DonM