Just interested to know why you were not overly impressed with King Henry's or Bablake? Although my son will be going to Bablake senior in September,he attended mainstream Primary,and received no extra coaching,except the usual extra homework from me. Obviously you want the best chances for your son,because getting a free good Grammar place these days is like gold dust. Personally, i would just find a good primary school for him to go to then get him extra tuition. This site looks good,and there is great support from the forum. In the long run you would save yourself a lot of money. Put it towards fees you may need when he goes to senior independent! Thats if he doesn't secure a place at a Grammar.
If you are looking for a prep school to prepare him for the 11+ then there is Coventry preparatory school or Devonport Lodge(i think that is the correct name). They both have websites. Good luck