946000- Chim is something a Daedra knows of, yes. When confronted by it at Vivec's trial, Azura reacts rather distastefully. If Bal knows of it, then the others know as well, because they are all equals, each a Prince. The Xarxes was a false account, penned by Dagon, who did not take part in creation, so he can't know how to take Mundus on its Endeavor.
Didn't say they didn't. I said that Sermon 12 wasn't a sufficient source proving all Daedra know of CHIM. The Trial is a better one, however.
And how can you know what CHIM is but not know how to go about it? To me that's kinda oxymoronic: that's almost like knowing that 5+5=10, but not knowing what a plus sign is. To quote Vivec, "none [of the Princes] held [the Tower] in...high esteem" when they saw it, which is an important idea regarding the state/process of CHIM.
I also thought the Mysterium Xarxes was a guide to bind oneself to Dagon's realm, not necessarily in getting/going through CHIM (specifically) or general apotheosis. If the former is true (which I currently think it is), then I say Mankar succeeded and the Mysterium Xarxes is quite true.
And, just for the hey of it, you can read http://www.imperial-library.info/fsg/kikaiarticle1.shtml if you want.