hmmm if you want something that will be interesting to a classical or musical listener then I wouldn`t say much of the stuff quoted by anyone here is in that category.
Most of the above is loopy.

You want something very polyrythmic with maybe some interesting key interactions.

I would say some of the more experimental mills stuff maybe.
Some of the stuff by the 65DMavericks was also quite musically complex.
Some of the later detroit stuff?
Innigo Kennedy`s Asymetric MP3 releases maybe?
Or perhaps something by Autechre or Arovane