little problem

hello i post earlier an topic with the question how i transport my shizzle from my mpc to my computer.
i found an way to do it, but i hear it double when i record it at audacity
HOW CAN i fix that?

instead of recording it on audacity you can recored it back into your computer by going to mode record and select main out instead of analog or whatever-- bad thing about this is that its gona take the space of your mpc if you have enough left. what your suppose to do is buy an audio interface to use inorder to record in to the compuer. be more specific with your answer its way to general and hearing double dont know what you mean

i mean if i press record in audacity and play in my mpc
i hear the sound from the mpc 2 times together.
so i must mute something i think in my computer or in my mpc.
but how can i do that
i have an eMU 0404 Sound card.