1.If you open ROM files with proper explorer as 3dsexplorer, you can see its structure.
2.Since we don't have keys to extract data DECRYPTED from files, we can neither do extraction from its internal.
I means, ie, romfs may contains what you want, however no keys for extracting that so you can not get it decrypted.
and then you can not even try to find something inside.
important Keys stored in key-scrambler not nand so maybe only hardware helps. That's all (i know now)