My children have been at the Academy for several years (one is still there) and I don't really recognise the description put on here above. For a start there IS a grand piano in the main school building! And my son was always allowed to play in break time at school concerts etc.
Both of my kids are musical and very into drama and they have plenty of opportunity to do both. There is an annual school show - Oliver this year - which is a whole school affair. Every single child takes part and it is always an amazingly high standard. One of the Founders is a classically trained pianist who manages to get the children to learn a whole show in 3 weeks - and they thoroughly enjoy it and really work as a team.
There is an annual carol concert where children who want to do solos (instruments or voice) can perform and every class sings a separate carol with mini solos for those who want them in each song.
My daughter loves to sign, dance and act and she feels like she does plenty of music at school - weekly singing sessions with her class for example. She also has the opportunity to write and deliver speeches and recite poetry in English classes.True there is not an orchestra but that does not mean the school is weak on music and drama - I would say it is in fact very strong in that area.
I do not agree that boundaries do not exist or that the discipline is poor - it is in my opinion very strong and there are very clear guidelines which the children understand. I think it is easy to mistake this because the children call the teachers by their first name and because the school does not have formal parents evening, much uniform etc. But the children are very clear about the rules and I can avow that any bullying is stamped out immediately. The head teachers will always respond to calls/emails even out of school hours if there is a problem and deal with issues straight away.
It does not have all of the trappings of a traditional school but what it does have is in my view far more important and extremely hard to find. It is a very nurturing, kind school which builds up a child's confidence, teaches them tolerance of others and teaches them to think. Each child is treated as an individual which enables teachers to help each child achieve to the best of their individual ability.
My son joined after having a terrible time at a much sought after NW3 school - he was too individual to fit in and was utterly miserable. The Academy teachers built up his confidence and within a term he was a completely different child - happy, confident, taking part in all aspects of school life and thriving academically.
And last but not least the teaching is extremely good! Much better than any other private school my kids have been in. The teaching is rigorous so your kids really understand what they learn and can then apply concepts to think for themselves.
Looking at your description of your son I think you should seriously consider the school. Personal experience leads me to know that he will get fantastic teaching that pushes him as much as he is capable, chances to take part is sorts/music/drama and yes even trips - and all whilst his confidence is built up and he learns to get on with and value all sorts of kids with differing levels of ability and talents - all useful lessons for life!