Two active disks cost you 10 to 16W. Why are they active?
Not the best for super low power consumptions, but at the moment not your main problem.
Undervolting is nearly useless for idle power consumption. It influences only high CPU usage.
Disable array auto start, remove both components, spindown your HDDs, execute powertop and check if this influences your PKG states. If yes, find out, which of both is your problem.
Ask the biostar support. If their answer doesn't make you happy: Throw it in the trash.