you might have to export each object separately depending on the material and give them a basic material in your rendering program. I imagine it would be tedious to line everything up again but maybe there's a way to convert the coordinate system between the two programs

>>1007480 (OP)
if its proper topology to work with, then it shouldnt be much of an issue to unwrap it, but youre probably better off just using shaders

>>1007480 (OP)
Use Ptex ehe

>>1007480 (OP)
One approach is to separate the model into more simple shapes. For instance, make each gear a separate model. Auto UV tends to do better on those, but try it on one to see if it will work for your needs before you do the whole thing. Then you just shrink the islands for each individual UV so they will all fit in one, and merge the models again.

Another way, I've only ever used substance design to make basic tileable textures, so I'm not experienced with Painter. But I guess how I would approach it in Blender is to split the model into 6 "cube face" sides, top, bottom, left, right, front, back, and project each side from the ortho view into a UV. You'll get stretching, and it still requires some seam-work, but it's a huge shortcut.

Ultimately, if you want full control, quality, and freedom, you'll have to do a retopo. Or wait for AI to get good enough to do it for you.