Unless there are motherboards that integrate an Envy24 chipset (which would be awesome), you can still get improved fidelity from a separate sound card... Just having 7.1 channel support and having a coaxial/optical jack is irrelevant if the audio chipset is not very good. Ports != quality. Being on the same bus as the modem is also not particularly relevant, especially if you never used a modem; no longer having a modem doesn't automagically make the audio chipset better technology.
The Chaintech AV 710 is not quite as good as the more expensive Envy24 chipset cards (eg:
m-audio revolution), certainly, but it beats integrated and Creative chipsets. I think you underestimate the Chaintech though... I seem to get real sound quality from my $20 Turtle Beach Santa Cruz (an older envy24 budget card) connected to my stereo speakers. Certainly the audio chipset is only one component involved, but it doesn't hurt to go for the best..
For reference, if you want to approach studio-quality recording, you will probably want something from
E-mu, not Creative.
Anyways, the point was that you can get better quality sound for less money than buying a Creative card. Or you could get much better quality for about the same money. If you are happy with your integrated chipset, then by all means, don't throw money away on separate cards.