Stuart: Given that your room sounds like a nice batcave, then I wonder if your brighter scene issues might be to do with gamma. The HD series is known for the gamma dropping well below what it is marked at (2.2 often measures less than 2.0 for example). This will give you better shadow detail perhaps (maybe too much even) but will make the brighter scenes washed out. In a batcave a '350 should be able to take a measured 2.3 gamma and that was how I ran mine when I used the 'tent'. I used to compare lower gammas with the calibrated 2.3 setting on paused scenes and there was extra 'pop' and depth compared to 2.1 or lower pre calibration. Nothing for or against the Darbee in this case, but the base calibration might help, then add the Darbee on top.
Secondly (and a use for the Darbee which might help): I used to find that any sharpness or detail setting above 0 on my old '350 would cause a very slight 'micro judder' most noticeable on end credits, but must have been there for other moving objects too. Try setting the '350's sharpness and detail controls to 0 and if necessary increase your Darbee's settings instead: It may give you the sharpness you want, but without the motion effects. Certainly worth a try anyway, or some combination of the two device's settings. The '350 tends to create 'halos' or ringing even at very low sharpness settings, whereas the Darbee apparently doesn't so might be preferable to use the non ringing sharpener.
The above is also an example of how a proper calibration before adding a Darbee might get more out of the overall set up rather than trying to use it as a band aid to fix something that isn't really broken: The Darbee could then enhance the resultant image perhaps with lower settings, or perhaps with even better subjective results.