The Unity of Experience in the Upanishads

The Upanishads admit that the self is a kind of hidden underlying subject, which is quite hard to access. And I think that if I were the Upanishads or if I were a Vedic thinker and I wanted to reply to this, I would probably go after the Buddhist in two ways. The first way would be to focus on the identity or the self of the subject at a given time. It's rather a simple quality of experience. But when you abstract experience, that quality is a sort of nothing. That quality is part of the flow of experience, but it's not a thing. So that it's a nothing.