Not a problem with onboard sound nowadays, maybe with cards that are 3-4 years old (SB 16) etc.
I use onboard sound from my Shuttle and my ASUS and have no hiss problems whatso ever. The ASUS had some engine noise because of the inverter, but I fixed that with a good case ground.
The shuttle had the same problem, but dissapeared when I powered it with an OPUS.
I use an old PCI SB Live value (4 channel) in my Epia V8000 car setup, and I reckon it sounds very good. I have an Audigy 2 ZX in my desktop and I don't think I notice a huge difference. The onboard sound on the Epia was absolute rubbish, no bass would ever come out clean, and the levels were too low. Epia M's have much better audio apparently.
I use my SB live in 4 ch mode feeding 4 channels into Kicker crossovers mostly to pull the levels up a bit before they hit the amps. Sounds great. There is background hiss when nothing is playing though.
I've tried a cheapish no-name USB sound card (admittedly with gold-plated terminals so can't be too bad) in my car and it had NO hiss at all and sounded quite good. I believe things like the Xitel pro audio link may be good for you, USB, and has RCA outputs, but USB will always have standby and CPU issues, and so I'll probably stick to my PCI.
I downgraded from my Extigy to my FV24 onboard sound while I was troubleshooting something.. Yuck.
Some onboard cards are ok, but you can't go wrong with an extigy.
thats kinda funny, in my car, using onboard sound from a laptop no less, I still find that audio source plays the largest role in quality of sound.....
and its a cheapy compaq armada, to boot......
audigy NX 2
Simple my freind, get an audigy 2Nx. They might have some small issues, but damn they sound good. Only card on the market that supports DVD-A and 24bit decoding, in CMSS 6chan audio. I have a brand new but medium install in my new car (four new pioneer speakers and 2 12inch subs) and when I play the THX test them under the audigy showcase program, my freinds's jaws drop!
Had some other sound cards in my earlier installs but this one ****s on them all.
It allows you to play some music that your used to hearing, louder, because on other systems as the finer frequencies your used to distorting at higher noise levels, ....dont on the audigy. And you can listen to it even louder:)