Sorry for the slow reply, had to dash off to Cairns for a few days to test the new 2015 Best gear!
We use 2 models, UHO38SX-2NB and UHO507SX-2NB
Switch your helmet on and select a channel, put the helmet on, then flick through the radio channels until you can hear someone talking to you, if it sounds like you talking then you've found the right channel and you are good to go.