I used to have an 5.1 speaker system connecting to integrated 5.1 sound card. It works fine and all the sound coing out in one Jack to Subwoofer and then in Sun woofer, there is amp an lines out to 4 surround speakers.
But now I got an board with 7.1 HiFi integrated sound card. It has seperate line for Sub woofer and 3 line * each line for 2 speaker: back, front and surround). I do not know how to use my speaker system.
Standard analog 7.1 connections are just regular 5.1 analog connections with one extra jack for side channels.
It should be front left/right, rear left/right, side left/right, center/sub.
Where as 5.1 is just front left/right, rear left/right, center/sub.
If you only had one cable going to your sub though it was probably a digital connection. What speakers and sound card do you have?
They are all integrated sound card in mobo. The 5.1 is Abit IS-10 and the 7.1 is Gigabyte GA-8I915P-G.If you look at the Gigabyte manual, you will see that there is only 4 jacks for speaker out put while in my Sub, there is 4 öine out for 4 surround speaker. I do not know how in Gigabyte mobo, they combine each TWO speaker (front, bach and side) in to just ONE jack.
All the pics of the board I can find show 6 audio ports and the manual describes them to be in the same config I have described above for analog connections (including mic and line in).
The manual stats: Line in (blue), Line out (front left/right, green), MIC (pink), Back Speaker out (back left/right, black), center/sub out (yellow), surround speaker out (side left/right, grey).
That board also appears to have spdif in/out but it likely only supports 2.1 output so you will be better off using the analog connections.
Please have the IS-10 manual downloaded(!!). I put the jack into the green blue line at the bottom. in fact, I do not care much about the sound card. After you ask me, I have a look at that and it seems that there is a black, square one at the bottom of the 2 x3 placement but it is not open, there is a light in it, just like LAN light.
In fact I was quite surprised sine all the sound system I have installed from PC, there is always just ONE line out