They might maintain that, but I just don't see how they can maintain it without contradiction. We think of the numinous as being transcendental in some way. If it's simply the result of the operation of chemicals in our brain, I don't see how it can be particularly transcendental.
Well art is not about positing testable theories (though some psychologists/neuroscientists are trying to do that)... art is ultimately about creating art, and trying to convey inner experience. So art involves observation but it uses it to entirely different ends.
I'm defining materialism as the ideology that only the physically-observable exists. This means that there art and the inner experience it conveys is also just the push and pull of atoms following scientific laws, nothing more.
Arguably quantum mechanics says that a lot of what exists, does so in states that cannot be observed since observation changes them, but Maxx might justly jump down my throat on that because it is a very outmoded way of looking at things.
So moving on. You seem to be confusing the idea of whether something has a material basis with its existence. There are a number of phenomena that exist as the results of arrangements of other phenomena but which acquire qualitative distinctions from their constituent parts. Indeed, it can be argued that the entire universe exists in this process of aggregation and arrangement.
Atoms are arrangements of particles in energy states. The arrangement acquires characteristics that do not exist in the particles themselves. Thus quantum mechanics gives rise to atomic physics.
Atoms interact with each other in complex manners to create new structures: molecules.
Thus atomic physics gives rise to chemistry.
Chemicals interact in a vast array of complex possibilities so that immensely complex structures can be created out of as few as four varieties of atoms: Carbon, Hydrogen, Oxygen, and Nitrogen. Thus Chemistry gives rise to Biochemistry.
These complex chemicals interact in even more complex ways, producing structures of ongoing interactions unlike the structures that they are based on thus Biochemistry gives rise to Biology.
And so on. At each level in the process new amazing phenomena come into being in a variety not necessarily predictable from the level below.
I usually say that we live in a harmonious universe, where the simple constituent parts can be arranged in enormous variety by building level upon level. Just as notes can be arranged into chords, chords into the pieces of individual instruments and the playing of individual instruments can be arranged into symphonies.
The point is that each level of phenomena has three different levels at which it can be examined:
1. What makes it up and how is it made up?
2. What does it itself do?
3. How does it interact with other things to create a higher order of harmony?
Phenomena may have a material base (for a given value of material) but that does not remove the experience of the thing itself.
Knowledge of food chemistry and nutrition do not remove the taste of food, but they can help in deciding what foods are a good idea to eat.
Knowledge of harmonics and acoustics do not destroy the experience of music, but they can help in making instruments and designing music halls.
The transcendental experience, the numinous to quote Hitchens is a matter of direct experience. It doesn't have to be connected to something beyond the human in order for it to be an elevating human moment. The mind can be opened by an experience, understanding and emotion wash over us, and we come to see and understand more then we did before. Just because the underlying events for this are neural firing and brain chemistry no more removes the experience then knowledge of organic chemistry destroys the taste of lunch.