Seems like there's enough spare CPU cycles even if some of them have been used for your written-in-Javascript IDE and written-in-Javascript messaging client.
One of the problems with WinModems was they were sensitive to CPU load. In the nominal "browsing" case they might be fine, the average webpage wasn't going to load down the system too much. With something like gaming where the system was more stressed the modem could have weird latency issues or the driver could even crash.
I still have mp3s with botched (and very audible) grabled parts, corrupted at downdload.
It's less about total cycles and more about
scheduling. You don't really want a real-time
or low latency thing like sound to get preempted
by another process.
Integrated sound cards are way more susceptive to interference, though, and the quality suffers a bit. They're merely good enough.
Also, people generally seem to use USB sound cards, as it removes even more room for interference (though my ASUS Xonar Essence STX sounds great already, unlike the integrated solution that transfers power rail and other noise).