For 'experimental drone/ambient-like/random/generative stuff' you will need many modulations. In a small case, DivKid Ochd (8 Lfos in 4HP) is worth considering.

The Ochd is great and on my wishlist ;) Waiting for some second hand one popping up.

I looked up a few matrix mixers now. From the looks and build quality i would prefer the Doepfer A-138m, but it's quite huge in 20HP. The next ones are the Bear Modules Matrix with 14HP and the AI Synthesis AI008 in 10HP but "only" 4 in 3 mixer with a seperate sum output.
From those three i would say the Bear Matrix is the best option, but than i'd have to swap my Black Stereo Mixer with a A-138s, which i think is too small. The AI008 looks a bit confusing from the layout to me...