"mic in and line in, whats the difference. Is there a severe difference and does it really make the music sound better even on my horrible soundcard?" -
Yes, ESPECIALLY on your horrible soundcard. Almost without exception, any soundcard that does its conversion from analog to digital signal INSIDE the computer, will have very large amounts of noise picked up from the electrically noisy environment inside the computer. There are a couple of high end cards that this is LESS true of, but they cost as much as an external sound card.
When you input a mic signal, which actually can be as low as -60 dB in level, into the preamp? of a soundblaster, you're giving all that electrical noise a 50 dB (about 400 x) headstart on destroying your signal-to-noise ratio. You will hear a large difference in sound quality, even with a cheap external preamp, by plugging your mic into the external preamp and taking the line level output into the line input on your soundblaster. Now, not only are you bypassing the cheaply built preamp in the soundblaster, but you're coming into the computer with a 400X stronger signal and amplifying it that much less. This keeps the noise from the computer from being anywhere near as prevalent in the sound.
Whether you use a mixer or just a preamp, as stated by others above do NOT use the mic in on your soundcard unless you just like garbage... Steve
