Hello, i do have some old home theatre system around, it is a samsung,is 5+1, and it has 2 cables that i must plug them into my pc to play music . One is red one is white. There are the only jacked connectors. I must plug them into an Asrock fx990 extreme 3 . i have allready headphones, mic in and the line out for the headphones are taken then. i do have some other connection on the mobo, but i really dont know where i must plug those 2 cables from my home theatre.
What kind of headphones are you using? Are they amplified? I'm asking because you are using the line-out jack for the headphones. The line-out jack is typically reserved for connection to an amplifier, such as your home theatre system.
In any case, you need a cable that will convert the Red and White "RCA" connection to a 3.5mm round jack that will plug into the line-out of your motherboard.