Internally in VSIG, the Surround Mixer and System Positioner both support up to 50 inputs and outputs, so the limitation is just the 8 I/O limitation at the Algorithm level.  Chains support up to 32 I/O, and you can define up to 32 I/O in VSIG for the algorithm, it’s just that the H9000 won’t load algorithms with more than 8 Inputs or Outputs.

Anyway, outside of Eventide, it’s possible to do a surround micropitch, but Blackhole is not available in VSIG. You could do other reverbs though.