The manner in which a physical state is said to
produce a mental state is where the two models diverge.
There is the general distinction between form and matter, where the principle of action is said to be from the form itself. Socrates is constantly saying things like: "Physic does the work of the physician and carpentering does the work of the carpenter"
There is also the context which the attunement of the musical instrument appears, namely whether the soul is immortal or not:
"The body is held together at a certain tension between the extremes of hot and cold, and dry and wet, and so on, and our soul is a temperament or adjustment of these same extremes, when they are combined in just the right proportion. Well, if the soul is really an adjustment, obviously as soon as the tension of our body is lowered or increased beyond the proper point, the soul must be destroyed, divine though it is---just like any other adjustment, either in music or in any product of the arts, although in each cease the physical remains last considerably longer until they are burned up or rot away. Find us answer to this argument, if someone insists the that the soul, being a temperament of physical constituents is the first thing to be destroyed by what we call death." Phaedo 86 b
To argue that mental states are irreducible attributes of brain states is to stand on this side of the argument. When the brain dies, so does the soul. One of Socrates' argument for immortality is to see "mental states" as not being dependent upon corporeal premises:
"Well, said Socrates, this does not harmonize with your view. Make up your mind which theory you prefer----that learning is recollection, or that soul is an attunement." Phaedo 93 c
The rest of the arguments, including the one I quoted initially, are directed against the analogy of attunement as what a soul does. Adding "brain states" to one of the elements being controlled by the soul is putting the possibility of mind as coming from two sources that have been framed to be incompatible by definition.
When I said I was comfortable with the "physical" model, I didn't mean to say that it was the last word or explained everything. I am saying it is consistent with its own premises. I am objecting to overlaying this model upon Socrates' because the action doesn't give itself enough problems. It dismisses what it doesn't want to include and includes new things without their introduction requiring any work. I am not dismissing the difficulty of seeing mental states as physical and something else at the same time. This approach looks too easy to me.