If you're not restricting yourself to hardware, the Patterning iOS app is a non-4/4 drum machine seeker's dream. Circular interface, each track has individual step length (1-64), subdivision, rotate, direction, etc. It sends out MIDI velocity/note per track. You can import your own samples. Sound editing is pretty basic but it's the sequencer that's really killer. You can automate most parameters in the sequencer as well, again, per track.