If you use a sky dome it must be the light emitter. The much easier way is to use one of the IBL pre-built scenes that come with Poser 13.

Load the "Wide Street" scene from the included content. The scene looks like it's just a simple light dome. It's way more.

This scene is built so the dome is visible in preview. So, you can see what you're doing with the dome and pose the scene relative to the environment.

When it renders is uses some Stupid Poser Tricks (tm) to hide the visible environment sphere the render is using Cycles native environment. (which isn't normally visible) The orientation of the preview dome and the HDRI environment are linked. You shouldn't really be able to tell it switched.

If you want to use a different IBL just use the same HDRI on both the light and the dome. You can do this in one act from the Texture Manager by "Replacing All ... In scene"

How the magic works ... You absolutely don't need to know how this works to use it. But if you want to build your own here's the secrets ...

The first stupid trick is that the Environment Preview only shows in Preview. It doesn't render.

The environment preview is only there for composing the scene. It's orientation is linked to the BG Environment node in the material room. That make the Cycles native HDRI environment line up with the Preview. Just to make it more interesting the BG Environment Rotation is in Radians.

The orientation of the preview IBL light is setup the same way. Just like the Preview Background the Preview IBL doesn't render. It's just there so you're not stumbling around in the dark. Just for nerdly fun this one is UVS to Degrees. Ewwww math!

So every thing you can see in that scene in preview, none of it renders. Not the light or the environment sphere. They're just there so you can see what you're doing. All that actually renders is the BG Environment node. It creates the light and the environment.,

BUT WHYYYYYYY!

The cycles BG Environment simple isn't capable of not casting shadows. Took me a while to wrap my head around that too. But it's not a "light" so it doesn't have shadows. It's a diffuse emitter and stuff that's occluded simply can not receive light.

So at the end of this we get to the point. If you use an environment sphere Image Base Lights will not shine through it. Period, Full stop. Ain't happenin'. The "environment must go into the Cycles BG Environment node. The "dome" must the hidden when rendered. Also absolutely none of this apples to FireFly. It's not a physical based render. That means it's allowed to break the laws of physics.