5.1 Speakers with Microphone possible?

Hey guys, I have a sager 8170 with a Realtek HD sound card. I recently got some 5.1 speakers which I love, but unfortunately, the speakers arent allowing me to use my mic in. Here is my current setup/options. I have 4 3.5mm output ports.

Speaker config: 5.1

First port
-Front Left and Right Speakers

Second Port
-Center and subwoofer
-(has a mic/in)

Third (unused)
-(Side speaker option)
-(S/PDIF out option)

Fourth Port
-Rear Speaker
-(Line in Option)

Please note, I have tried switching the rear speakers to side speakers, and then using the line in function. Does not work. Any suggestions?