Sounds like Atlas missle level technology (Surprised actually) and I believe the subs are noisy as hell. But, it just takes one hit to spell a total human and economic disaster in the US. Even the though of vaporizing one US city is a pretty big deterrent for the US, regardless of the ability to counterstrike.
Conventionally, China is making a great effort to upgrade its forces, but the naval focus of an invasion makes that much easier to counter by Taiwan. IMO PRC is likely uparming just to keep its threat and intimidation potential hight.
Charon