Northamptonshire has borders with Warwickshire to the west and Buckinghamshire to the south, but Northampton itself is quite a long way from the GSs in either county so even though it's possible to apply and sit the tests, getting a place could be difficult as distance is one of the main allocation criteria - for Bucks, at least. I would definitely recommend looking at Northampton School for Boys for boys living in Northampton as it has an excellent reputation (I suspect their special subjects are drama and time travel, their most famous alumnus being the current incumbent of a certain tardis!
). As mentioned in Herman's post, a few places are allocated on musical aptitude, so certainly well worth considering for a musically inclined boy - and there are also some places reserved for technological aptitude. Most places allocated randomly though, so a bit of pot luck is involved. Northampton School for Girls in Spinney Hill has excellent facilities for music and drama but I don't really know what it is like academically. (Not to be confused with Northampton High School for Girls which is an indie.)