Hi Stuart,
You can use both, webbrowser or hardware switching.
In the IO settings of both RRCs use "on/off" mode.
If you go to the radio RRC webbrowser you can simply click the 3 on/off buttons.
The corresponding IO ports (see pin out in manual) will pull to ground.
Also, if you connect one of the IO lines to ground at the control RRC, the corresponding line will pull to ground at the radio RRC.
The only thing to overcome: the allowed current on these lines is limited.
You can solve this by transistor, optocoupler or reed relay switching as a buffer.
I use small 5V reed relays just because I had some laying around.
Similar to
http://www.conrad.nl/ce/nl/product/504599/Reedrelais-5VThe (+) of the coil is connected to 12v over a 1,5kohm resistor (to compensate the overvoltage), the (-) is connected to one of the IO ports. When the IO port is activated it pulls the (-) of the reed coil to ground and the reed relay switches in. The little reeds supply a voltage to larger relays.
It is all really simple, just try.
73
Paul
PD0PSB