The manual for my X-889 says that doing this increases your output voltage and creates less heat with better SQ as a few stated above. I notice a huge difference when I turn it off and on.
I know you mentioned kenwood already, but my X789 has the feature too. I think the entire(or at least the majority) of the eXcelon lineup have this feature.
as far as i know it can't.....but if it can wanna tell me how to do it?
....i didn't know any pio units had this feature....some of them (p9...possible p1r) don't have an amp...but i dont 'know any that have an amp and can shut it off....