2 amp blocks with 4 channels each = 8 amps per patch (2 simultaneously)
2 cab blocks that load 4 ir's each, that can be mixed/matched any way you want. 4 channels for each cab block = 16 irs per block = 32 cabs per preset (8 simultaneously). 2 ir player blocks per preset that load a single ir x 4 channels each = 8 more ir's (2 simultaneously)
So 10 cab irs and one tone match block can run simultaneously in one preset while having an inventory of 40 cabs instantly available through channels.
There are over 2,000 factory ir's and over 2,000 user ir slots
There's more cpu horsepower (2 -3 times that of the II) available for more complex effects, more effect instances, effect chains and routing and more complex amp modeling.
The interface is a huge upgrade from previous units
Major usb audio interface upgrade
The effects upgrades/additions are almost to numerous to count