Sorry I canít be of more help, but with all my retro style helmets I use in-ear speakers (flare pro audio).
For the short time I had my Hedons, I could not figure out a way of getting a comm system in without ruining the liner or scratching the (stunning!) paintwork. So I just always use in-ears.
Granted, i didnít try too hard to find a solution as in the back of my mind I knew the comm would ruin the sleek lines of the helmet.