I find your story interesting.

Perhaps try (harder) to get the covers off and try plugging or unplugging the ports?

That's a sad situation, for sure. I'll be interested to hear how the conversation with the installer goes. I mean, what do you do if you say you're unsatisfied because the subs sound horrible, and he says "they sound fine to me".

I'm sure there must be "good" inwall subs, but they are probably expensive.
bibere usque ad hilaritatem