Thanks for replying, you're very helpful!!!
Dry? [I hope I can explain this]
Well, piano's sounded rich. Whereas our X3 doesn't. Example, when play a song, the piece doesn't give rich melody or harmony. The song sounded dry like there is a vacuum. It doesn't boost, it sound dead. Let me give you an illustration -- When play a notes C or sound "DO". The sound should be "DO" with echo/vibration at the background [I'm sorry I don't know how to describe it] but our sound is like "DO" and then it dead. With pedal on, it sound "DOOOOOOO" with long sustain without rich "DO" like a piano. When playing few chords progression with pedal on - it doesn't sound rich as a piano. It's dead or dry.
BTW, the X3 default setting for effect is Chorus.
Manual?
Good question, unfortunately we have misplaced the manual .

We have try to get an extra copy from our local dealer but they said they don't have any

.
Room?
Our Church setting is a long shophouse with a capacity of 150 chairs. Cement wall. ceiling about 20' high.
Boosting the EQ?
Well, we have try everthing. We did off the reverb and put everything in the middle and still the sound doesn't boost. We try increasing the high slowly and still none of them satisfying.
Our amp has 2 inputs, volumn 1 & 2, low, mid, high and reverb. That's all.
I think you're right, perhaps the amp couldn't handle keyboard's frequencies. Korg, I think it still one of the hi-end keyboard/synth maker but I would say Roland still the best, no doubt.
I hope these give you little knowledge. If you need more information please ask.
Thanks