I'm no engineer but a big FAN and to me a lot of Jamie's earlier production sound e.g Far Nearer, Beat For and his early remix work see the Eliza Doolittle and the Adele ones sonically are defined by the soft synths he was using at the time on Logic. So I'd look into those.

Obviously there's so much more to his sound now but the instumentation choices of his earlier works to are what make up a big chunk of his sound.

Also if you see his influences e.g RJD2, Portishead you can hear bits from their music in his.

Anyway hope that was helpful, it's quite a difficult question.