can you make your assets into 2D PNGs? as in literally just flattened pictures as in the pictures provided on the page? I only use 2D, sorry. :)
If enough people suggest this feature, I will add it to the asset pack :) In the mean time, here are my suggestions:
This asset comes with the tileable rock texture you see in the images which you can most likely use inside any 2D editing software to create your sprites. If you want to make isometric looking sprites from the 3D assets, you can use a free 3D editing software such as Sketchup to position the assets and render out as sprites.
Hope that helps!