I have the Enspire direct wired from my mac computer via USB to midi input. It works beautifully. There are very cheap cables available but it is not advisable to buy them as they often play with dropouts. Get a known brand name such as Roland, for perfect performance.
I use it to OPTIMISE midis for perfect playback, always at 70% full volume, which is 3.5/5 yellow lights on the control face.
1) YES, all midis will play on it – even those with no piano track, as they play thru the loudspeakers under the piano.
2) There IS software to convert mp3 or wav to midi and you can trial it for free but it is but it gives very disappointing results and is costly. An analogy is that trying to create midi from an audio file is like trying to reassemble vegetables from vegetable soup: It works better the other way around. What pieces have you in mind to convert? I may have them converted already.
Thousands of great files are available on the internet for piano – particularly classical piano pieces from old reproducing piano rolls which have the full expression of dynamics and phrasing encoded into them.
I can direct you to various sites for collections.
Write direct to me wam(at)ram(dot)net(dot)au