Thanks for the recommendations. The two Friberg books are on my to buy list as well as Elements of Desserts. I suspect I'll use the latter more than the former. My only concern about Migoya's book - is to purely focused on plated desserts? I normally make entremets and layered petit gateaux, I don't tend to do plated desserts as I need to take what I make into work as so I don't end up with clogged arteries and the size of a house.
Are the Hermes books (apart from the Dorie ones) in English? I wish pH10 was in English, that book looked awesome.
I was recommended So Good as well but what I have seen of it, there isn't the explanation (the why) I'm seeking. As gfron1 suggests, I think I am after a cross between a textbook (which should provide the why) and a cookbook (providing the up to date recipes and techniques). I don't want something that's dry. My local patisserie supply store recommended So Good Recipes and Ramon Morato's Chocolate. He preferred Morato's book over someone like Paco Torreblanca's tome as the former explained a lot - alas both are incredibly pricey.
He also suggested that the next step in my learning is to understand ingredients and how they work. This is so when something does go wrong I understand what has happened and why and what to do/not to do next time. Is this something I'll be able to get from So Good or other sources?