Nice blog Magnum
I use in helmet speakers and have done so since the 1970s when I got my first bike with 12v electrics and fitted a car cassette player in a waterproof box to the bike
Now I am using an Autocomm wired system which I've had for more than 10 years now, it has a link for the Bluetooth output from a TomTom GPS and inputs for music and 2way radio with Vox/PTT selection on the handlebars.
It is way out of date now the latest systems are Bluetooth4 and you have everything integrated into the helmet.
As I have just put my ride up for sale and looking to downsize and go a bit more off-road orientated it's all moot at the moment, I've had this bike for 10 years and up until last year used it a lot.