If you were to try it, get the discus first and let them get well established. (Let them "own" the tank for a month or two before adding the angels). Then get angels which are smaller than them.
I also wouldn't try it in anything less than a 40g.
Angels can attack discus. if you get groups of each then the angels should spend most of their time chasing other angels and not the discus. Also nake sure they have lots of room. A 75 g would be nice for 4-6 discus and 3-4 angels.
I wouldn't do it. There has been 'stories' about Angelfish being carriers of a disease that doesn't effect them, but does infect Discus. I won't argue this issue since I have already read both sides of this issue and I'd rather NOT chance it.
Also, as mentioned above, I wouldn't stand for an aggressive Angelfish. There will be NO attacks on my Discus!
Both Angelfish and Discus should be the "stars" of their aquarium.
It's purely an aesthetic thing, but they're both (potentially) big, showy fish and I just feel they shouldn't have to share the spotlight with any fish other than their own species. Not to say they can't have tankmates, just that those tankmates should be smaller.
'course, in the case of Angels, if those tank mates are too much smaller, they'll become lunch