I don't own one, nor have ever tinkered with its menu. But, I have discovered some information regarding specific settings to make sure that your blacks are not elevated when outputting 24p.
At first I thought that such reports would be the fault of my Onkyo 805. It isn't. Anyways, I know a lot of you know your equipment very well, but I'm SURE this post will help somebody out.
PS3's 24Hz setting to Automatic (as opposed to On).
SuperWhite to On.
If not set to Automatic, its possible, at least with Onkyo, that ALL of your other HDMI source-inputs will be negatively affected as well.
Crazy.