My computer is equipped with two sound cards, the integrated one on the motherboard, as well as a Soundblaster Live I installed myself. The Soundblaster has a special front panel with midi ports, and a volume control for the output. For some reason unbeknownst to me, the analog output on the back panel of the Soundblaster is only sending left side sound, so what I want to do is send sound from both the integrated card and the Soundblaster, so I can have my headphones plugged in the front of the Soundblaster, and my loudspeakers plugged in the integrated card in the back. Unfortunately, Windows only seems to have support for one sound output device at a time, so I was wondering if there was any other way of doing it.
The problem with onboard audio is that it doesn't always play well with dedicated sound cards. I would recommend that you turn off your onboard sound device in the bios and get some hardware that connects to the soundblaster card to drive both the speakers and your headphones. Many PC speaker systems, like the logitech X-240 -link below #1-, have a little satellite device that sits on your desk. It usually has both volume control for the speakers and a headphone jack.
If you really want to use your current speaker system, you can get a little "Speaker/Headset Switching Hub" -link below #2-. These devices plug directly into your sound card and then run the sound for your speakers. The only down side is that most of them only support 2.1 sound, not surround sound.
A third option would be to get a USB headset. The downside of this option is that you have to change sound hardware settings when you want to use your headphones. I have friends who use this option and it seems to work well.
If you want to use your front panel audio ports, I would look and see if your soundblaster card has audio headers. Look for "Intel HD Audio Compatible Front Panel Header" in the specs. I don't think the cheaper ones have it and the more expensive ones sometimes come with something you put in the drive bay. I think all the X-Fi cards have it.
Keep in mind that you could have some faulty hardware somewhere if you only get sound out of one channel. I would try testing out each port with a known good set of headphones and see what kind of audio signal you get. If you have surround sound, you may be plugging into a rear channel by accident.
Hope that helps
Links (New users can't post multiple links)
#1: Go to logitech's webpage and go to the speaker+audio section. If you look under speaker subheading, the X-240's are at the bottom.
#2: Go to amazon and search for "Manhattan-Speaker-Headset-Switching-Hub" it's the only result at $9.99 .
Only thing I know of that might do this is Pulseaudio.
Sink being output. It's not in version 1 yet so caveat hacker.