Wow! That looks like it caught on fire! I can see things much better in this last photo. If that board is charred through the traces then it is finished. There "are" ways to restore the traces, but might not be worth the trouble, kinda depends on how attached to the sub you are. I never consider what something is worth to sell, only what it's worth to me to keep.
If you had a local repair shop that is like I used to take things to 20 years ago, then I'd fix it. That electronics store owner became a good friend. Those kind of shops are rare these days.