The lighting result of Lux depends on many, many things. Almost impossible to right down in a short comment.

My first tip however, would be to replace the spotlights with small meshlights positioned at the place the spots are now. Spotlights give razor sharp shadows and with small meshlights you can 'steer' the softness of the shadows.

Luxrender lights are very different from the Daz lights and you cannot automatically convert a Daz light into a Lux light. I know that Lux picks up pointlights, distantlights and spotlights but my advice is to avoid those. Use the lights that are designed for Luxrender otherwise you are selling yourself short.

There is also no need to use 'houselights'. Simply disable 'Preview lights' in the 'Window' tab. That way you keep a clear overall lighting in your scene if you stil decide to keep using Daz lights.

Not much, but I hope this will set you in the right derection. :)