If the angels are a pair then the only way to prevent breeding would be to give them conditions that they are not comfortable breeding in (IE: Lowering the temperature to 75-76). This will not necessarily stop the breeding either, they can continue breeding in modified conditions regardless.
Angelfish that spawn are not necessarily going to produce fry, the female will spawn and if the conditions are not suited to their liking, they will either eat the eggs or the male will not fertilize them. Any changes in their environment could prevent breeding for x amount of time, but since they are a pair, it is most certain they will continue breeding again at some point. It is very common and well documented that they are very aggressive during "spawn mode" and can and sometimes will injure fish that pose a threat to the spawn, regardless of their intent to actually keep the spawn.
If you are seeing no signs of aggression towards the other fish in the aquarium then I would continue watching just to make sure (you seem to have that down pat already), as Angelfish can (and usually are) very aggressive during mating periods. They will spawn every few weeks and as I described above, the only way to stop this would be to make drastic changes to their environment and this will not necessarily work (nor do I recommend doing so, as it puts unwanted stress on the pair as well as other tank mates).
If one is being overly aggressive towards the other than I can only recommend you add additional hiding places for the one that is being picked on.
I will not go in to the angelfish<->gourami portion of this thread as I do no have any desire to tell you what to do with your fish, if things are going as you want, then I say god speed and good luck