If there are enemy submarines operating in the Yellow Sea, something has already gone very wrong.
There's a narrow-ish chokepoint between Dalian and Shandong, which presumably has seabed sensors.
The Yellow Sea is enclosed by Chinese territory, so it should be a bastion where Chinese aircraft and ships can use active sonars as much as they want.
The Yellow Sea is pretty shallow and small so there's nowhere for a sub to hide, once it has revealed itself.
In any case, the Yellow Sea is that small that only 1 deployed Chinese SSK makes sense.
If you look at other shallow areas or choke points, they are further away and more exposed to enemy submarines entering.
So SSKNs would make more sense.
---
And what would an enemy submarine be trying to do in the Yellow Sea?
If it's going after a Chinese SSBN, then that SSBN can release a radio buoy and request air support to flood that target zone, if there is even a hint of an enemy sub.