I don't mean to sound rude, but you actually know what CHIM is?
Though they have the potential to be, the one[s] with CHIM aren't necessarily masters of 'everything'.
In very basic terms, when you have achieved CHIM you are everything, and everything is you. However, you still remain your identity. So, it's I are we, we are I, but I am I. Zero Sum is similar, but without the I am I part, and you disappear. Zero Summing is what happens to the Moth Priests quite often. Vehk Vehk achieved CHIM, wrote how to achieve it through his love letters and his sermons. The dwemer tried it by absorbisiding their entire race into the giant stompy robot they made. It...sorta worked, except the issue of powering it. It is believed that Talos also achieved this.
The big named Lorites know about it a lot more.
But, for all intents and purposes, I'd say we should leave out Vivec out of this discussion, since he's a blasted thief.
For the original question, I'd say Dyvath Fyr, at least for ones alive. In history, Sotha Sil, D-F, or some Psijjic we have yet to know about