Of course Jonathan is much closer to Simon than I would be, but I am assuming that he plays on a Mark VI soprano with a soloist-style D mouthpiece and 3.5 reed based on his particular beautiful tone, which shares many characteristics with that of David Roach and Daniel Gauthier.
That's my speculation, but you can contact Simon yourself! His website is
http://www.silentage.co.uk. Please, Please let us know the setup if you find out -- I think he's one of the best soprano players ever.
Angel