Well, after failling asleep for about 5 hrs unexpectedly I took another look ..
Change that block of layout code I mentioned to the following:
Lua Code:
elite_icon = "Interface\\AddOns\\nUI\\Layouts\\Default\\Art\\nUI_HUD_EliteRight",
rare_icon = "Interface\\AddOns\\nUI\\Layouts\\Default\\Art\\nUI_HUD_RareRight",
rare_elite_icon = "Interface\\AddOns\\nUI\\Layouts\\Default\\Art\\nUI_HUD_RareRight",
world_boss_icon = "Interface\\AddOns\\nUI\\Layouts\\Default\\Art\\nUI_HUD_WorldBossRight",
It was the wrong path before to get to nUI's main art files