lol you can mix discus with angels. i used to keep my discus with altum angels. most of the time articles you read online are just from their experience. im sure u heard how difficult it is to keep discus too right? well....wrong. discus are easy to keep. i treat them like any other fish. all u need is common sense.
reason why people say discus are difficult to keep is they start out with BAD discus to begin with. so when they die they think discus are hard. cuz most of those people buy discus from fish stores that most of the time carry low end stunted cull not so healthy ones. buy them from a good source that has healthy discus then ur already a big step ahead. and chances of running into problem are very slim. unless you just bad at fish keeping.
the only fish that lives up to articles saying they are hard to keep are altum angels.