The GWIII has discreet input selection codes, as well as discreet on/off codes, so it might be reasonable to assume that the GWIV codes would be more or less the same.
Incidentally, did they move the IR sensor on the GWIV? The positioning of the one on the GWIII wasn't that great, particularly when trying to use the remote that comes with the set (super narrow IR beam?). Of course, in order to use discreet codes, one needs a third party remote anyhow, so the remote that comes with the set becomes a non-issue in such a case.