OK, I've found out what produces my problem with 4.2b, I checked it with metal_rock style; when Audya is powered all styles play perfect, including metal_rock. Then I pick a registration which includes metal_rock style and guitars are gone. Go out of registration and pick the same style directly - no guitars again and no guitars in practically all rock styles.
So it seems 4.2b in my case is somehow not compatible with registrations made under 4.1b
I believe this incopatibility will be gone with new sounds from pen drive. If not I have a problem which only Ketron programmers will have a cure.
Regards,
Luka