Some things you might want to know about onboard & dedicated soundcards
* Adding a card with its own sound processing takes off load off the
processor. It will allow your CPU to perform better.
It will be around 15% CPU utilization for onboard vs 5% for a dedicated
one. CPU Usage may vary across different processors/motherboards.
* Sound varies depending on what kind of hardware is used in onboard
& dedicated ones, which will affect the sound output.
Like some give HD sound output but others will give just High quality sound output.
* You might be getting the occasional hiss/disturbance from your speakers
when using your onboard. The dedicated ones will be free from this or
will be much better than onboard.
* Sound Output also depends on the Type of speakers (Stereo, 2.1, 4.1, 5.1, 7.1) you have & Quality of the speakers
* Depends on what it is being used for. Like music, games, movies, etc
Regarding your question, here is the thing.
You have Realtek ALC883 with 5.1 HD Audio.
You are planning to buy CREATIVE Sound Blaster AUDIGY Value Sound Card, which is 7.1 with High Quality Output.
So you are asking which is better, it depends on the type of speakers you are having & what you are using it for.
Since HD will sound better than High Quality, I would go for the onboard. But dedicated have their own advantages as said above.
I would recommend you to go for AUDIGY 2 Value instead of AUDIGY Value since Audigy 2 Value has HD output & would perform way better than Audigy Value.
So here is the final order of preference in terms of performance.
1. AUDIGY 2 Value with 7.1 HD Audio
2. Realtek ALC883 with 5.1 HD Audio
3. AUDIGY Value with 7.1 High Quality Audio
This is my view, Anyone lemme know if I am wrong.