A SSK has the ability (which a SSN, like 688 LA, Seawolf or Virgina doesn't have) to shut down their engine completly, and simply float around. This makes them completly silent (well, at least almost completly), up until the point when they fire their torpedoes. This means that a Yuan can detect a SSN if it's floating around, or moving very slowly, under 5 kts usually for a SSK. USN claims that the Seawolf has a silent running capability up to 20 kts, but no one knows how silent that is.
When facing a surface vessel, however, they (the surface vessels) usually use active sonar, the 'ping' you hear in every submarine movie, which works more as a radar. This only works short distances, and is therefore mainly a defensive measure, since a sub can hear it at longer distances than the surface vessel who used it can get a usefull echo back (compare this again to a radar). But, if a SSK waits for a CBVG to 'run over' it, then it will be found by active sonar, usually before it will get a good target motion analysis (TMA) of the carrier. Also, the Chinese Sea is HUGE, which means that a fleet could slip through a SSK 'net'. Here factors like satelites and reconnaisance comes into the picture.
Bottomline: no one knows for sure until it's tried.