As Nick said, they both have two DSP processors. Each of them can run one algorithm or you can use the monolithic mode to run one algorithm using both the processors.
The main difference is the types of algorithms that you can run on each processor. You'd have to build the kind of algorithm your example mentions (a phaser to ch1+2, a pitchshifter to 3+4, a reverb to 5+6 and delay to 7+8). But it is possible to do it.
If you're wondering what you can do with an H8000, I would recommending downloading VSIG with the H8000 module definitions and see what building algorithms is like. The H8000 is like the ultimate modular effects system I've ever found. The TSR-24 from Digitech is the most similar thing that I can think of that you could build algorithms on but it doesn't hold a candle to the capacity and capability of this machine.
