This is an example where it would not be possible to eliminate the roof and use your EnvSphere for lighting.

This rendering I got it with only two lights.
EnvSphere for external light (but I did not apply any image) and a small light to support the interior of the room.

Obviously I had to work a lot on materials, thanks to your advice and your BBGlossy

Rendered with FF

Poser Pro 2014 SR 1 on Windows 7 64 bit
I use IDL, Gamma Correction and EZSkin for all final renders.