Could be one of many things my friend, here are some suggestions:
-Detuned: Your piano sample (its a sample right?) may be out of tune, you may be utilizing it like it is a C note, when it is not, this means you may be playing in two different keys, and can sound awful.

-EQ: It may be as you said, an eq problem. Try lowering the frequencies used by other vsts. Avoid using a 7 band eq, or any other eq with a set bandwidth. I suggest EQing with a parametric eq, this way you can squeeze the piano in, if it is clashing with another sound on a simular frequency.

-Key: Make sure you are playing in the right key for all sounds.

-Levels: Try lowering some of the more overpowering sounds. Avoid boosting the levels on the piano, especially if you have a compressor on the man fx channel. Also maybe try panning it more to one side to give it more freedom in the stereo field.

I hope that helped, if you posted a sample of what the problem sounded like, myself and others could help you much more.

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Thanks! Played around with it and managed to fix it
Cheers.

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