Don't forget that the mic input on a Soundblaster has a restricted frequency response. It's not really intended for hifi recording. Always use the line in as that has a wide flat response. The best way to go is to use a mic amp or a mixer with mic inputs as freddynl suggests and plug it into the line in. At the very least, use a mic transformer (about 1:10 ratio) and plug that into line in.

Bryan