I'm going to build a new pc soon but I got a little confused when it comes to the sound card. I own these speakers Creative Inspire T3030 which are 2.1 and I already have a sound card. A program from CPUID identifies the card exactly as Sound Blaster PCI (it's very old because I got it about 4-5 years ago). The MOBO i'm going to buy is the Asrock Socket 1155 Z77 Pro4 or the H77 Pro4/MVP which both have the same oboard sound: 7.1 CH HD Audio with Content Protection (Realtek ALC892 Audio Codec), Supports THX TruStudio.
Will the onboard sound be worse than the sound that my pc produces now with the old Sound Blaster PCI?
Should I buy the Asus Xonar DG or go with the onboard and not waste money?
In all honesty, for casual music/video and gaming, onboard sound these days is fine. I still have my Audigy XS in a draw somewhere which I got in 2003 and I noticed a huge improvement, especially in games with surround sound back then. I still use a 5.1 speaker setup, but the onboard sound is more than ok now and I wouldnt put money into a sound card unless you were doing things like music recording or rigging your PC to a high-end receiver, but even then you would probably just use HMDI/optical.