Wombat,
The signal strength of your radio was good, no need to touch that or the antenna. Easy test, set up two bikes a K or so apart, test 1 used helmet. test 2 use hand mike plugged in. Im betting test 2 is fine.
SR10 does have some settings that can be changed, just plug in to your puter via a USB lead. Update the firmware while you are at it. Also, see if you can change the settings in the Scala, it may have a setting for mic gain
Dont try messing about with the radio, you could bugger it totaly.
I have been thinking about Rays problem as well, and I think he might be suffering from poor audio input as well, as I was able to talk to him over about 15 to 20Ks, but he had poor audio..