Trying to make actual sense out of the DNA reploid thing is nearly impossible. Every living thing has DNA, even viruses have DNA as well. However, DNA inside of a robot is something that is...nonsense. But to go with the flow, when DNA changes--it's is not an evolution. At all. It is a mutation of it's structure. Mutations are caused by radiation, viruses, cellular meiosis, or errors in DNA replication. When that occurs, the host of the mutated DNA has to change to accommodate the mutation. However, that doesn't mean that the result is always positive. In fact, most results of this process tend to be negative, the host's structure tends to be rather confused of the mutation, and can overcompensate, or even cause several key cells to undergo apoptosis.
All things considered, from sheer statistical odds, X's body should have rejected his constant mutating DNA and his body should have gone through a computerized apoptosis. DNA and a soul cannot be the same thing. DNA refers to the chemical, organic, and mineral structure of an organism. Meaning, that all that makes X, function wise is in his DNA. However it'd be ridiculous to say that the soul is there.
A rapid mutation in DNA would never mean anything positive coming from it. Well... in MOST cases.
Edit: I should add, to be fair, that the slim chance that DNA undergoing rapid mutations, and it turning out well tends to leave the host nearly impervious to certain illness. So, if considering the small chance that X IS in that statistical impossibility in my opinion, that would explain his near immunity to the Sigma virus. It could also explain why he explodes from being saturated by too much of it. His body would initially attempt to adapt to the virus, but would fail from the sheer amount infection and X would indefinitely undergo apoptosis---I've noticed that I have yet to explain it's definition. But "Programed Celluar Death." Seems fitting of a name, if you ask me.