This post is for modders. It won't be useful for someone looking to just use mods.

For dual-wielding, the k_male_skeleton_01.hkb used for all humanoids has a less than ideal tuning of the left-hand weapon.

These skeletons https://dl.dropboxusercontent.com/u/32649007/Dualwieldskeletons.rar  improves the location where the off-hand is visible by providing the game with a new bind point for the weapon for k_male_skeleton.hkb. You need to put the extracted .hkb file in the /Gfx/ folder. Since it is an overwrite, it works retroactively for all unittypes with that skeleton. The locations for the other skeletons' off-hand location are unchanged, but they need to be included (so the off-hand appears for troll hero, iron golem and juggernauts).

An example can be seen here: http://i.imgur.com/53D29BQ.jpg

After you've included the .hkb in your /Gfx/ folder, replace

              <GameItemTypeModel>
                    <ModelFile>gfx/hkb/Weapons/W_Axe_01.hkb</ModelFile>
                    <Texture_All>gfx/hkb/Weapons/FE_Weapons_01.png</Texture_All>
                    <Attachment>hand_left_Lcf</Attachment>
                </GameItemTypeModel>

with

              <GameItemTypeModel>
                    <ModelFile>gfx/hkb/Weapons/W_Axe_01.hkb</ModelFile>
                    <Texture_All>gfx/hkb/Weapons/FE_Weapons_01.png</Texture_All>
                    <Attachment>hand_left_Lcf_special</Attachment>
                </GameItemTypeModel>

in your modelpacks.