With the environment texture (cycles node), you can use an HDRI directly by plugging it in the Background node (Check Cast Light in the Background node). This was explained in the link I posted.

If you use EZDome instead, make sure you have created the sphere (sphere button in top row). After creating the sphere use of the presets provided in the link in the manual or create your own preset with your own HDR textures. Optionally create a EZDome sun in EZDome (first tab)

I prefer EZDome because it is easier to use and the results are pretty much identical. EZDome adds rotation, collor and intensity adjustments and allows you to separate environment from lighting. The HDR maps provide the lighting pretty much the same as Octane does and most likely Carrara as well. So far i have not heard from anyone that EZDome fails, so let me know the steps you are making where it fails, so i can notify snarly

Here one example where I used EZDome