Oh cripes.
"I think the issue here is that the OP is convinced that her DS is deprived, despite, along with each and every one of his siblings, and his parents, having had the benefit of a very expensive and exclusive education (regardless of who is paying for it, and how), and is deserving of some sort of 'inner-city scholarship'."
At no stage have I ever said or intended to suggest that my DS is deprived, or in need of an inner city scholarship. 
He is fixated on Eton, and is going for a music scholarship + bursary. My question was whether we needed to do anything about this before Year 8. Several posters have given me some fantastically useful advice on this score, all of which I will be following up.
Joan, your longish post seems just mean. We are, I repeat, looking at a scholarship plus bursary. Eton fees alone would wipe out over half of our income. This doesn't make us 'deprived'; it just makes us, like the vast majority of the population, unable to afford the full fees.
If he does go there, I think he needs to go as a music scholar - because the school is so good on the musical side as well as being academically excellent. If he isn't up to an Eton music scholarship, I would look closer to home (my take on this is that if he wants to go, and can get his scholarship/bursary, then I support him one hundred percent, even if it's not what I would necessarily have come up with left to my own devices). The other option is specialist music schools, but I am reluctant to shunt a boy who's academically very good too down a strictly musical path. A music scholarship to a superb school with an extraordinarily good music dept seems to keep more options open for him in the future.
It is by no means the only school that offers fantastic musical and academic facilities. However, it's the one he wants to go to.