I don't know that much about Robinsons, but what I have heard and read is that the standard ICS system is very poor. You can't adjust the volume for each headset individually, and if there is any mismatch between them, one will be almost inaudible. It seems it's the cheapest thing they could get away with. You need an upgrade to it in any case.
I'm sure actual Robbie drivers will be along to give more specific, and perhaps more accurate, advice.