You will often find piano transcriptions of popular music pieces. In all other cases, you will have to achieve this work yourself. Or just try out if the original score sounds well on your virtual instrument. You will possibly learn that some pieces sound well as if they were originally written for the piano while others apparently show unwanted artefacts or generally produce an unpleasant sound.
The reasons for an unsatisfactory sound are manyfold. As a listener, you will have your expectations. For example you will like a tremolo on a violin, but when played on a piano, the sound feels unnatural. You would possibly prefer octaves as a tremolo. Or you would prefer a voice at a different pitch.
An important point to consider is the fact that different instruments may play the same note at the same time. Espressivo is able to detect and remove common notes, but the question remains which note should be kept. Turning on MIDI Polyphonic Expression (MPE) might mitigate the problem without solving it completely. As a final resort you might consider editing the score. To give Espressivo a hint, place the less important note in brackets.
Sometimes, it is just not the appropriate instrument. Try an other one or design an instrument yourself using a software synth.
Did you experience any problems when trying to play scores written for non-keyboard instruments? Let us know.