Tangible metaphysics is an oxymoron by definition of metaphysics (something beyond/above physical, i.e. tangible). If it's tangible, it's not metaphysics. If you can subject it to the scientific method, it's not metaphysics. Your EEG experiment is nowhere near metaphysical, it's as positivistic as can get - you very crudely measured cognitive load using EEG.
Well, of course, if you consider psychology to be metaphysical, you are only partly true - Freud, for example, can be neither validated, nor invalidated. Skinner or Pavlov, however... and anything published in respectable journals for the last 30 or 40 years.
Why can't the metaphysical interact with the physical and be detected that way? Most of science today is like this, indirect observations of reality we cannot perceive with the naked senses. If the brain is the metaphysical mind's antenna, then my EEG experiment is observing the mind's operations through the waves it generates in the brain. What remains is to determine of those waves can emerge purely within the brain, or if the waves are beamed in from elsewhere, i.e. the mind. Analogous to looking at my TV antenna and determining whether all the TV channels are being generated by the antenna alone, or whether the antenna is receiving them from elsewhere.
I honestly don't understand why these sorts of ideas receive so much friction. I cannot think of logically coherent objections to them. They seem very scientifically testable to me.
> Why can't the metaphysical interact with the physical and be detected that way?
Because then it stops being metaphysical and becomes physical.
Now as to your central problem, conciousness being beamed to brain. The reason why it gets so much friction is that it flies agains a massive amount of tangible evidence and research that brain generates conciousness. It also falls to Occams' razor very easily (like the idea of ether medium did - a PhD in electrical engineering should know this). And in it's core it is basically the same as "soul" - intangible, immeasurable, unknown entity with scientifically unknowable properties.
In order to bring it from the realm of metaphysics (matters of souls, virtues, etc - read Thomas Acquinus and continue towards antica via Augustinus to better understand what metaphysics is and how it is different from scientific knowledge), you have to propose both a full hypothesis on how this "brain as a receiver" works, and a set of reproducible experiments to show your theory to be true.
Jesus Christ, I never thought that I, a person with no degree, will ever explain the basics of epistemiology and scientific method to a PhD on the internet...
A necessary property is 'aboutness'. Consciousness is always about something else, or perhaps about itself as in the case of self consciousness. No material object has any inherent reference to anything else. For example: the words in this comment are nothing but pixels on a screen. However, we interpret the words to refer to the content of the idea I'm trying to communicate to you.
