So, brossa , if I’m getting you right, you want rhythmic complexity in a context of slightly extended classical harmony. So, going through the mental rolodex -
Bartok - check out the ‘Concerto for Orchestra’, the ‘3rd Piano Concerto’. (From your responses, I’m guessing you’d find the String Quartets or the ‘Music for Strings, Percussion & Celeste’ kinda harsh.)
No one has mentioned Bernstein yet, and I think there’s lots for you there… ‘On the Waterfront’, ‘On the Town’, ‘Slaughter on 10th Ave’, the ‘Divertimento for Orchestra’
John Cage ‘Sonatas and Interludes for Prepared Piano’ Yes, I know Cage’s later works are as weird as they want to be - this set is early and cool, using the piano as a semi-melodic percussion instrument.
Harry Partch - Harry Partch : Barstow, In It's Many Flavors is a site I just found while checking the exact title. The wacky tuning system is at the core of his aesthetic. Drives some people nuts, others love it. I’m in the latter category, but I understand the viewpoint of those in the first. Rhythmically, it’s fabulous.
You might be interested in some of the Spanish and Brazilian composers of the 20th century - Manuel de Falla, Isaac Albeniz, Heitor Villa-Lobos. My tastes and recommendations are rather guitar centred, but de Falla’s ‘El Amor Brujo’ or the ‘Sombrero de Tres Picos’ are a good start. Villa-Lobos’ collection of ‘Choros’ are great fun.
Leo Brouwer (Cuban) has many interesting compositions (Avoid ‘Canticum’ - I adore this piece, but the opening (flail the snot out of one of the harshest chords ever heard over and over on the guitar for six seconds, be silent for six seconds, then do it again for ten seconds - I’m not allowed to practice that one with anyone else in the house because it gives the kids nightmares). Maybe try ‘The Black Decameron’ for a start.
Another thought - I don’t know where you are, but you might want to check nearby ballet or dance companies, because it sounds like you’re verging on the kind of stuff that interests lots of contemporary choreographers. Not too discordant, but with lots of rhythmic interest.
Anyway, that’s a start. Happy listening…