This has been the single biggest struggle I've had with studio since I started using it. If you look up posts under my name you'll see a bunch of questions (and answers I got). In the meantime, the problem with the maps is that they tend to have baked in lighting and light probes. This skews things a lot. Short form, DHH is supposedly easier to use but Graphicsmod is far more complex and capable. It also lets you use Hanmen's textures which really help in some cases. Most commenters will try to steer you to graphicsmod but ultimately it boils down to what you're looking for and how much tweaking you want to do.
To get you started off, check out this helpful post on
reflection probes
The only other thing I can suggest is check out other's scenes and see how they did their settings.