if you want to save sound from your piano playing, why not you just record directly from audio out of the piano into audio in of your PC? then convert the wave file into mp3 to make it smaller

agreed that u should stick to midi. anyway to answer yr question about connection, u don't have to put a mike in front of the piano's speaker. that will pickup external noise as well. yr piano should have a line out or headphone jack. connect it to your sound card's line in. then adjust volume (piano & PC). i'm sure your PC has some kind of wave recorder software which comes with the soundcard. then get a freeware wave to mp3 converter

soft compared to what? audio sound too soft could be many things.