Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150807010020/@comment-37.152.33.225-20160202161432

I think the Emperor gaining some knowledge from them is enough, and fits with grimdark. He then uses said knowledge to create the Primarchs, which would also fit with some of them being 'tainted' from birth. And could also be a plan of Tzeentch.

The Emperor gaining is powers from the Chaos gods is just stupid though, and quite simply, does not happen.