Is it possible to finish the Domain of Anguish quests with heroes? What are the tactics/builds?
Yes it is (or was) doable, and actually someone posted a screenshot on Guilgwarsguru forums right within a exzessive discussion on beating Domain of Anguish (DoA) and Fissure of Woe (FoW) alone only with heros. See this guildwarsguru Thread.
But I would advice to not attempt this unless you are REALLY experienced, it requires HUGE amounts of skill, in my opinion.
Someone also posted his complete build on pvxwiki. It says this should be foolproof but I have no personal experience with it.
It is in fact, feasible to do a hero run of the DoA.
HOWEVER! Doing so requires luck, skill, and a really precise setup, perfectly tailored to all areas. (The mission itself is much harder. However, going solo can allow you to cheat at the end a little, but it requires frame-perfect timing to keep the gate open.) (Fun Fact: In Hard Mode, Mallyx the Unyielding is actually one level higher than his own god. Or any god you fight. At level 33, though, he isn't the highest-leveled creature in the game.)
As for the Fissure of Woe, that's a lot harder, since you can't cycle out parties. Hope you can micromanage seven people, because you are going to need it.
The Underworld, on the other hand, is a whole 'nuther kettle o' fish. Since the Skeletons of Dhuum started to appear, it's gotten progressively more hostile.
In other words: Go all out with the consumables. Use everything you have to defeat the impossible challenges. And don't feel afraid to flee or to catch your breath.