onboard sound generally isn't very good. it requires AT LEAST a line driver to boost the signal voltage enough to be worth a damn.
It depends. What other audio equipment (speakers, amps, HU, etc...) are you running and do you consider yourself an "audiophile" or more of a normal listener...?
I agree completely with the last two posts.
What are you using it for? If its jsut for like warning sounds and fun beeps and such...dont bother upgrading. If you like the sound from the board also dont bother. If you want crystal clear sound like a theater well then there are more things to consider.
If the sound is clear but weak or just not loud enough consider other audio parts such as amplifiers or a new head unit. Sometimes its the speakers that cause the problem. Try the sound through a nice headphone set. If its clear is pobably speakers or head unit.
If it is the board. I suggest a USB sound card. They are small and light. And can be purchased online (eBay) for 10 to 20 bucks. The sound from the one I use is EXCELLENT, better than my desktop's Creative Live! Value (yeah i got the value version...big mistake...) Any generic one is good. Mine is simply says 3D-Audio on the outside.
If with the usb adapter it still sounds like crap...you may want to look at the audio system in your car. crutchfield.com can give some great simple inexpensive tips to enhance your cars audio potential
But hey...even with the BEST card....the road noise can be enough to destroy a good song.....
The onboard sound on my VIA EPIA PD mobo is just fine. Sounds great on an alpine HU w/ subs and upgraded speakers in stock locations. No buzz, and w/ road runner the EQ in Winamp gives plenty of adjustment.