The easy answer is take any piano sound you have and add effects, such as reverb.
You didn't mention what edition of x2 you had, but Producer came with Dimension Pro and True Pianos Amber.
Dimension Pro has some decent piano presets, some with effects already added. Amber is a great modeled piano that you can add effects to. Either way it is easy to get an ambient piano sound.
If you just have the base edition of X2 without the extra content, just insert Cakewalk soft synth instrument "sfz" as a simple instrument track. When you open up synth properties you will see the rgc:audio sfz player interface.
Click in the "Open" box and there should be a file called "Dimension Mini Piano.sfz" in the path "C:\Program Files\Cakewalk\VstPlugins\SFZ".
For effects, try adding Cakewalk audio effect Sonitis:fx Reverb to the track. There are some presets in there to experiment with until you get your sound.