Practice and Experience

When we meditate, we engage with the kind of practice and experience from which the rishis derived the "Atman is Brahman" teaching and the Buddha derived the "anatta" teaching, although the latter was backed up with philosophical analysis and argument. Thus:

practice and experience are more basic than teachings;
teachings are guides to meditative practice, as Marxist theory is a guide to political practice;
both experiences and teachings derived from them differ.

However, we can synthesise apparently contradictory teachings. "Atman is Brahman" means that each individual soul is identical with the transcendent whereas "anatta" means that there are no individual souls. However, the Upanishadic teaching can mean instead that each individual self is identical with the one universal self whereas the Buddhist teaching can mean that there are no separate selves. In that case, the teachings agree.

Buddhists do not refer to a universal self and rightly if this were taken to mean that the universe is a single person. However, it need only mean that the universe is conscious of itself through many individual selves and this formulation is consistent with materialism.