What you call “transcendent mind” is the seeded data after big bang but before emergence of fundamental forces (as far as I'm aware, there is no scientific work that would elaborate on that though, on the other hand I didn't look exactly deep into it either). In Abrahamic parlance, that would be the “creator aspect” of God (or the famous Demiurge of Gnostics, though not evil as they insisted). Hindus call it Brahma, the creator god who was created first but forgot that he's created too (not to be confused with Brahman). Today, you could equate “transcendent mind” (some call it Akashic records) with the whole cosmos (see matter-energy-information equivalence).

Brahman (which is synonymous with God, consciousness, but also existence, infinity, etc.) is beyond concepts only in the sense that it cannot be adequately named. It cannot be pinned down as something distinct. It is everything and it is nothing. You cannot point your finger and say, “That is God.” Well, you could and it would be true, but only partially. If we would like to describe creation, the most appropriate sentence would be, “God Gods God's God.” As is obvious, it would not take us very far in terms of communication. Just as a side note, Hasidic Jews, too, maintain that there is nothing but G-d.

So to answer your question, world is God appearing as world. It's illusory (or not real) because “worldliness” is not its true nature. The true nature of God (and world) is the universal infinite (self-)knowing existence you know as the notion you have when you say “I am.”