It s the same number of inputs . 15 like the DRUMIT5 ... AUX ins are for other brands compatibility .
Quite sure you cant use them as 4 more inputs ...
I agree, the reason the Drumit 3 did not release years ago is because they wanted to make it "Universal". So my best guess is that the additional inputs are not to increase the number of pads/cymbals but to add inputs for alternate types/brands. For example a Roland 3 zone ride would require 2 inputs so I would guess you would use both A and B of the Cymbal inputs for that. A Roland 2 zone crash would require only one of the Cymbal inputs. A Roland Hi Hat would be connected with the HH controller to one HH input, HH cymbal to the other. But we will have to wait for further info to verify all the compatible pads, cymbals, zones, etc. But, hey, it would be great if those extra inputs could support additional cymbals/pads increasing the number of pads on your kit and you could assign any sound you want.
Edit, I think I can now confirm that the cymbal A and B inputs are still only 3 cymbals that can be connected/used. The additional B input is for modules that need 2 inputs for a 3 zone cymbal. Still pretty cool if you like 3 zones for all of your cymbals.
In typical Politcal style I will refuse to name my source ..... LOL.