There are no other options.
You can perform one-way sync to mirror it to the NAS.
Or possibly use the NAS as a computer, run calibre locally on the NAS (if it is x86/x64 rather than ARM, there are prebuilt linux binaries). Then Remote Desktop into the NAS to manage your library. It has been done, there were a handful of threads discussing this recently.
But the copy calibre works with must be on a physically-attached drive.
"some of the concerns in that FAQ don't apply to me" ??? Clearly, some of the concerns do apply, because you just tried it and got a corrupted database... whether your library is mutilated for one reason or two reasons is irrelevant, if your library is still mutilated.
And for the record, the reason that still applies is the main reason anyway.
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