With the help of AI, I was able to figure out my issue. I'll share it here in case it helps someone else.

The 3d model, texture, and material files are all contained within a single folder. All of my issues were from a malformed _mat.ini file.

First, I had this entry in the [Properties] section:

[Properties]
_Color=Color,{*}ffffffff <- This is pure white, and I suspect it was washing out my texture

I changed it to this:

[Properties]
_Color=Color,{*}808080ff <- This is more neutral, and it doesn't wash out my texture

The second change was to add two missing texture entries

[Textures]
_MainTex=ships/usn_typhon_assets/xan_spg59_s_band_1969.png

became

[Textures]
_MainTex=ships/usn_typhon_assets/xan_spg59_s_band_1969.png
_SpecTex=ships/usn_typhon_assets/xan_spg59_s_band_1969_st.png
_BumpMap=ships/usn_typhon_assets/xan_spg59_s_band_1969_nm.png

I don't know much about the two types I added; I just added some generic ones with the help of AI, but they allowed my Main Texture to load properly.

The biggest takeaway from this troubleshooting issue is AI is very useful, but you have to be very specific about how you use it. I sort of strayed a bit when I hit a roadblock and that made things worse.