I've found when soling raids (read: ony, 3D sarth, Maly) that Dark Apotheosis has interesting effects that are deeper than face value.
The first of this being that the armor bonus to you is lesser than the armor bonus to your pet. The 250% that you get from Dark Apo adds to your pet as well, and its substantial. I've found that Voildlord is an amazing tank but Voidlord while you're in dark apo is even better (I didn't know it was possible).
In addition, I've found that mastery is worthless because its almost always better to have your pet tank than you.
Good strats I've found are when I'm about to pull threat, I just hop out of DA and soulshatter and then pop back in. The only think you really even use fury for is Soul Fires and procs are few and far between. I've also noticed that Soul Leech + Corruption healing glyph = amazing. It lets you health funnel when needed without issue. I do not use soul link, its just super bad if you're going to let your pet tank.
For stat weights on solo tanking, I've been using Int >> Hit >>>> (they all suck for damage) Mastery > Haste > Crit
I don't always use Dark Apothesis, for burn fights like 3D sarth I just void lord, blow all cds, pop wild imps, doomguard, etc, and then meta at 1000 and blow the boss apart. For the ones that I do, however, I stay in Dark Apo almost the entire time, pet damage reduction is amazing.
But basically, the point of this thread is that I've found that tanking as Dark Apo is pretty much useless, and its just better to use the voidlord while under the additional armor effects. Dark Apo would be even better if it didn't let soulshatter taunt (condiering it doesn't work on bosses anyway).