Following the instructions, I've updated the iwave.h and iwave.cpp files using the official spectral responses from DigitalGlobe (In the iwave.h file I don't know if it's necessary to use more accurate wavelength ranges). Now I don't know how (and I don't have much time!) to go on the next steps.. (update geomcond files and recompile grass), I have never compiled a software!! :) Could someone help me? I can send you all the updated files, of course..