A good sound card is cleaner and clearer than onboard sound. How much you will notice the difference between onboard sound and a good sound card will depend on what you are playing, how good your amp/speakers are, and how good your ear is.
Originally Posted by future_computer
Comparing an AV Receiver with the best Sound Card, which one can produce the best quality of sound?
'Best' sound card? Doesnt exist.
Some AV/receivers have very good quailty sound, some of them are pure junk.
In some situations, the sound acrd will not matter at all (e.g. if you are bitstreaming the audio from DVD/blu ray via digital output, S/PDIF or HMDI). In those cases the sound card just passes the signal and doesnt do any decoding at all, its all done in by the receiver etc..
Originally Posted by jefro
I'd think that a dedicated sound system would outperform a sound card. A nice McIntosh system would suit me.
Apple mostly uses onboard sound, and its the same chips that are in windows systems. Apples wont sound any better than a normal windows computer.
With the extra cost of an apple system over a normal computer, you could afford to get a nice sound card.