I'm taking the approach of a mod to the board to limit voltage to the audio amp to 8V. (3 terminal regulator lm7808).
One cut in the right place and mount it to the back of the board.? Then the amp is no longer a worry.
The rest is either able to take much more or already protected by voltage regulation.? I see no problem at all with?
16.8V (4s2p Lion battery at full charge).
Allison