To resolve our paradox, it is first necessary to discuss a central concept in Toras HaChassidus, Ohr Ein Sof.
Ohr Ein Sof, literally translated is, the Light of the Ein Sof, G-d in His Essence. Conceptually, it is the "revelation" of G-d in His Essence.
It is called Ohr, Light, for several reasons: 1) its sole function is to reveal its Source; 2) it "spreads out" from its Source; 3) it has no existence aside from being the revelation of its Source, i.e., if the Source did not exist, the Ohr would not exist; 4) it has the characteristics of its Source (see below).
It is called Ein Sof because it is "unlimited," "infinite." That is, it is not called Ohr Ein Sof to indicate only that it is the Light OF the Ein Sof. But rather that the Light itself shares the characteristics of being unlimited and Infinite.
In addition, Ein Sof indicates that the Light: 1) is unlimited and Infinite is its "spreading out;" 2) is itself a simple and absolute Unity; and 3) it shares with, is similar to, its Source with regard to all of the characteristics described in Part 2 (not describable, except as the negation of its opposite).
Now we can begin to resolve our paradox according to the chiddush (innovation) of the Arizal and Toras HaChassidus.
The Creation of the worlds affected no change in G-d in His Essence because the Creation of the worlds was through the Light. Eiyee, we said that creation ex nihilo can only come through an Ein Sof? The Ohr, sharing with, and being similar to, its Source is an Ein Sof.
How then do we resolve the problem of their being two Ein Sofs and thus two Primary Beings - an untenable and self-contradicting position? No problem - the Ohr Ein Sof is an Ein Sof ONLY because it does share with, and is similar to, its Source, the Ein Sof, G-d in His Essence. It is not a separate existence in and of itself, but is only contained with, and the revelation of, its Source. Since its Source is Ein Sof, it is Ein Sof. But not that it is an independent, second Ein Sof.