For some reason I thought you'd tried him and been unimpressed. I generally prefer his early stuff but given your taste and your comments re: what you like about Mingus, I'm guessing you'll probably mostly appreciate Duke's late 60's-late 70's albums like "Far East Suite", "...and His Mother Called Him Bill", "New Orleans Suite", "Latin American Suite" and "The Afro-Eurasian Eclipse".
Ever listen to any Artie Shaw? One of my favorite swing artists and another big band with quite a few arrangements inspired by classical music. Here's one of my faves which I guess has become somewhat popular due to being featured on video game soundtracks and shit like that: