No intention of changing anyone's mind about the choices between speakers, helmet speakers and in-ear sources, just my experiences in the last 25 or so years of trying different solutions.
Back in '88 I fitted my K100RT with the BMW radio cassette player. I didn't fit the speakers because I didn't fancy sharing (or inflicting some might say) my musical taste on the world.
Instead, I had a redundant Sony Walkman headset that I realised the earpieces almost matched the recesses in the BMW System II helmet. I got one of our radio workshops blokes to make me a curly lead and NATO socket the same as we used at work.
It wasn't entirely successful as the position of the earpieces in the helmet wasn't quite right but I still remember sitting at some traffic lights bobbing along to the music, glancing left and seeing a bus driver alongside looking at me in a very puzzled way.
My next attempt years later was to use an Autocom connected to a Sony Discman and earpieces again. I would keep the Sony in the clear pocket of a tank-bag so that I could press the controls when I needed to.
Then came an iPod through the Autocom, again with helmet speakers. This was nearly the best solution but still a compromise between earplug protection, wind noise and music volume. The biggest issue was not having control over the content or volume of the music.
Finally I decided on some in-ear monitors and ditched the Autocom. The monitors have excellent sound reproduction and noise cancelling. I now just plug straight into the iPod and I have a little gadget that allows me to start, stop, mute, raise and lower the volume or skip tracks. Basically it's an adaptor with a controller I mount on the handlebars:
The buttons are not really designed for use with gloves but a well aimed thumb can just about do the job.
Probably the best things are that the monitors are designed as ear plugs to give protection and being able to mute the sound without rummaging for the iPod first. A bonus is that as the monitors are connected by the wires I seem less prone to dropping one or both when I take my lid off.