See i thought there were different types of gr2 formats and larian had their own type, So that wouldnt work. I might be wrong on that.. Just i have tried a few different converters from other games that work with gr2 and they always throw errors with divinity files.
Each Granny SDK has a slightly different version of the GR2 format, so there *are* different versions, although their format is similar.
I don't even know another model format that supports IK besides fbx
I haven't seen any sign of IK support in the current .gr2 files; what extra data do you need for that besides the usual "bones + weights + influences" thing?