Electric piano into passive board with active monitors question

[And I]

I know this may sound out of place but is the phantom power on or off?

phantom power does not exist on 1/4" ins and out. it's XLR only.

 

[And I]

You're not using TRS connectors, are you?

this is why i suggested plugging the cable half-way in to the board. if it's TRS and the keyboard can't handle that, plugging the cable halfway in to the board should make a good connection with the T and the S part of the TRS jack in the board.

 

[Aloe]

Is it possible you will need some sort of pre-amp to boost the signal from the keyboard to the mixer?

usually digital instruments provide either line-level signal via TRS or instrument-level via TS.
I have a Roland electronic percussion that appeared to be the latter.

no need for a preamp in that case, frankly, but if you dig the sound, it's also okay. but a DI would be enough, the mixer likely will expect a matching level on a mic input (unless explicitly switched to line level).