Just a quick update to any one who is interested, we almost have v3 of ExtrabiomesXL for 1.6.x updated.
Ignore the texture errors. (It turn out that it was not the development environment and was being caused by the change from texture packs to resource packs.) I am in the midst of restructuring my development environment so as to make it so that we can update v3 and do our work on v4 in the same place without one mod affecting the other and as such textures are not showing up until I actually turn the mod into something that you can actually drop in your mods folder.
Now that I understand what has changed API wise in 1.6 compared to 1.5 I can revert my test code for 1.6 and cleanly update it for 1.6, along with completing the few other bug fixes that I still have in our pipeline and the other small new features that we want to add as part of my taking over as lead dev for ExtrabiomesXL.
Keep your eyes peeled as we update you on what is coming in what we hope to be the last set up updates for ExtrabiomesXL v3 before we Finally move on and are able to release v4.