First, a quick lesson. All sound cards with the exception of a few have built in sounds that cannot be changed. (Cards like the GUS - Gravis Ultra Sound - can actually have samples stored on them that can be played back using sounds that were not originally on the card.)
All that being said - there is a distinct difference between MIDI and audio. Is sounds like you want to record audio.
For that, you would need something like Cakewalk Pro Audio.
For more information - before you spend several hundred dollars - try www.pgmusic.com
- look at a product called PowerTracks.