I think you have to look at how certain characters are converted from G3 to G8. If you use something like Riversoft Art Character converter (Using Scene Character script) what you get is a character that has all of it's morphs converted also. A heavily modified character (lots of morphs applied) like G3 Sophia has a lot of little defects introduced as not all of the integrity of G3 Morphs translate to G8. I only did my very first few conversions using RiverSoft's tool then completely changed my conversion workflow. It was almost impossible to get a true one-to-one conversion from G3 to G8 using only the Riversoft script. I never used the Zev0 XTransfer the same way, so I cannot comment on use in that scenario.
The second issue is a DAZ self created problem with the eye movements. Seems when DAZ created Base Genesis 3 and Genesis 8 characters they oriented the eyes 180° off and there is a size difference between G3 and G8 eyeballs (G8 eyeballs are physically smaller). All this and converting every slider causes almost all G3 to G8 conversions to look different from one another. They are close, but not exact.
They eyeball orientation issue can be solved multiple ways, the two most common is to reorient the converted eyeballs 180° and the other is to just not freeze the orientation of the eyeballs when you do an ERC freeze on the character morph. Not freezing the orientation will force your model to accept the default G8 eyeball orientation with the existing 180° offset.
Now this is how I fix the issue with models that use multiple sliders. I take the original morphed G3 and export it as an .OBJ file and then use Morph Loader Pro to reimport that .OBJ as a morph. You can also use intermediary applications to do the same thing (Hexagon, Blender, ZBrush) using bridges. Now I am only converting a single slider instead of 10's - 100's. My way still doesn't account for the physical difference in eyeball size, but in any render other than super hi-res face closeups, the difference is not noticeable. A consequence of any morph conversion is that they all have to happen at Base Resolution.
For the most part if you are only going to G8 you should be able to use the G3 texture maps without any issues, the UV Maps are almost identical. If you want to go to G8.1 then a Map Transfer from Base Female UV to Base 8.1 Female UV is in order.
I have been working on finding a workflow from G3 to G8 that keeps as much fidelity to the original model as possible. Without being a DAZ PA and not having access to the HD morph tools they have access to, I am pretty sure that my workflow is pretty close.
Are their better ways to do this? Probably.
Does this workflow result in a 100% accurate conversion? Maybe, Maybe not.
Could it be better with better tools? Definitely.
TLDR; Don't base whether a G8 conversion is good or bad if you use Riversoft Arts Character Converter. Too many variables exist to guarantee a perfect conversion. DAZ management thinks all their users are too stupid to use tools that actually work to create and modify HD morphs. Every conversion has compromises.
I am done with my rant and I need a nap now.
