[Dotol]

Try using an optical cable when using surround sounds systems that are 5.1+ more often than not it fixes many issues. Most songs and videos don't support 5.1+ audio but rather standard 2.1 and some audio receivers don't emulate the sound into all speakers. Raise your volume and watch this video:
http://www.youtube.com/watch?v=A4KYoQKAnoE

If it works you'll know that its working fine or you can search in youtube "5.1 surround sound test". Installing a brand new surround sound system on a computer without a sound card with included software can be a real pain in the ass, especially if its your first time and on top of that you have to deal with the very limited Realtek software, I learned this the hard way as I'm sure you can understand. Remember google is your friend, learned so much after a whole week of troubleshooting when I bought my system.

[Dotol]

Thank you for the fast reply but unfortunately I don't have an optical cable so I can not try this option right now I will buy one and update this post when I did it, I also tried many souround test on youtube and no one worked.

I think I might have to buy a sound card, does someone have a recommendation?

No, buying a sound card or optical cable is not exactly necessary but it can help in some cases or at least get rid of a lot of hassle. I'll try to help you out once my bf4 game is over lol

But yeah it looks like the settings in Realtek software aren't properly set up. Make sure its your default audio output, it should have a red checkmark beside it

[Dotol]

:D yeah installing those systems is a bitch but you'll find out that anytime something doesn't work its usually something you haven't done or done wrong enjoy ^^