Welcome to the forum!
To play your own samples triggered by MIDI you need a sampler or sample player, in which you load the samples on different keys. Then you use the sampler like any soft synth. I don't know if X1 LE comes with a sampler. If it does, the most likely candidate for you to find there is DropZone.
If you want to test with soft synths in general, I assume you have TTS-1.
At
www.kvraudio.com you can find lots of soft synths, both commercial and free.