nice work, have you considered rendering parts out separately . Render the background with the standard renderer, and then the snow using the path tracer?
not sure of the materials, but maybe a default shader ant the end of the shader node tree, and reducing for to around 1.35 around the for for ice and play with the translucency slightly?
Just an idea, this is 100 times better than what I could probably produce, but just a thought following on from what I use in Blender, as I think the path tracer would add some sub surface scattering as it does with clouds?
but again fantastic work
Simon