Yes, the Vijnanamaya of the Taittiriya Upanishad is the same as the Supramental except that the modern interpreters call it as the intellectual sheath. It is the same error with the word Jnana that is loosely translated into knowledge. But the knowledge as we understand is, in the spiritual parlance, an ignorance because it is based on division. It is agyana. So too the Jnana of the Gita and the Upanishads refers to the true knowledge, the essential or fundamental knowledge of the Oneness behind creation. This Oneness is termed as Vidya. So too Vijnana as we find elaborated in the Gita itself as the jnana-vijnana yoga is the knowledge of the Divine Oneness extending into creation. Vijnanamaya is precisely this extension of the One into the Many without ever losing the truth of the One and Oneness. Practically, it means knowing everything as the Divine knows it. It is a Divine Gnosis and not the human intellect and its error-prone inferences. It is a direct knowledge of everything by an inner identity.
Of course, the Supermind is not only this detailed knowledge but also the Divine Power behind everything. It is the Omniscience and the Omnipotence of the Divine, the Ishwara and His Shakti creating the play of the Ananda in the diversity of creation. There is a Supramental Love, Supramental Ananda and Supramental Beauty as well.
Affectionately,
Alok da
