no secret that i love dedicated sound procs. having said that IMO you will ALWAYS get better sound on a seperate card regardless of type over onboard sound b/c mobo has so much creating backgroung static/interference.
If you are only after having less work on your proc then you have to get a creative card or an (expensive) professional one. Creative is the only consumer level card w/ a DSP, all others rely on a codec and use the CPU just like almost all mobo based sound. Lots of ppl hate creative on this forum, but I have used them exclusively since 2000. I have seen many issues on friends systems that have been traced back to AC'97 codec drivers where I have never had an issue w/ creatives drivers. (NOT their other software, it sucks... JUST their drivers, you dont need the other stuff)
I know you said you didnt want to spend $100 but if you use primarily headphones then you will have best sound on an x-fi creative card. (read the toms review) but any creative card (even a sb-live 5.1) will take some work from your cpu.
I am not saying to only buy a creative card, just if you want to offload the cpu then that is your only option... that and I like creative's stability.
Now there will be many ppl that will flame me for all of this, as they did not read that last line... they will hack and hate on me for some statement that is misread... and if they dont then my perception of many ppl on this forum will raise a touch.
Well the current drivers for creative cause a nasty problem with asus update software. However there is a minor hack for it. Creative is sweet and the performance difference will be notable in the scope of things. Plus won't suck system resources like onboard.
If you use a PCI Sound Card, there will be a minor increase in performance, but not that much. Anyways some of the older Creative cards are good, just go to Newegg.com, list all, and then organize by Best Rating. Buy one with a price within your range, and really, get a set of speakers. I used to do the headset-only setup, and it was just annoying because I'd have to unplug them to get them into my MP3 player. Just a $40 or $50 set of speakers are fine, trust me.
Just another option... reality is as long as the card has 5.1 or more (the audigy is 7.1 above) and is a DSP (both sbLive and audigy are) then it is good and you will see an improvement. (sound quality and slight performance)
Sojrner is right. I would spend a little extra and get a better sound card. You won't regret it. One thing that I have learned in playing around in computers is not to overlook components. Things you think won't make a difference can make a big difference.
Back when I added I added my x-fi xtreme over onboard audio I ran a couple benches to see if there was a difference.
3dmark 05 went up 11 pts but having no audio on 05 the difference is really nothing. 3dmark03 that does tests with audio went up 215pts. The 24 sound test went up 3.5 frames per second.
I did think there was a problem in BF2 where some game slow down would occur because of sound, which was fixed when I added the audio card. I think the difference in frames can be bigger when you are maxing out the number of different sounds in game which well be exactly when there is a lot going on graphically.
remember that the 3dmark tests are generally graphics card tests, especially when you only have the free version. There is an actual pcmark test by the same company that produces 3dmark. There is a small impact as you say but you're not testing much with 3dmark.