Is nì- -us- productive?

[Plumps]

I wasn't sure if deeply would translate well here so I used thoroughly instead, I'm also not sure,

Why would nìtxukx be wrong?

Nìtxukx means deeply all right, but to use it in this context would only be correct if you are actually searching in a vertical direction, preferably below ground (or water).

Karyu Pawl's blog:

RENG and TXUKX
These words primarily refer to physical depth: kilvan areng, kilvan atxukx. They can't be applied to people: *tute areng makes no sense. But as in many languages, they are sometimes applied metaphorically to thoughts, ideas, analyses, etc.: e.g. aysäfpìl atxukx 'deep thoughts.'

So, in certain contexts we can use it in the sense of 'thoroughly', but I agree, nìno would be better here.

[kewnya txamew'itan]

Even if they can be used metaphorically, I think it's unlikely that such a use lines up with ours 100% so outside of those specific case outlined by Frommer, I'd avoid it. (Irayo ma plumps for finding that btw).

[Ataeghane]

Irayo. Now I think I understand it. I hope we will soon know more about it, but as for now tsaw tam.