I've done some more checking. I've just started to explore patch making on the River, that is how I discovered this. All patches seems to have the same level set for each voice, one patch may have all voices set to 0 and another voice may have all set to -10.
As I listen more closely there are 2 voices that are too high - voice 2 and 7. When I lower these two with -2 it is fine. I've tested for several included patches incl INIT and also my own patches. I believe this is caused by inproper adjustment of level on the 2 voice cards. I do not believe other Rivers have the same issue with voice 2 and 7, but maybe other voices - if so this may not be fixed by firmware but maybe by adjusting potmeter in the voice card ?