Hi Sam,
It is extremely unlikely that the problem is caused by the RRC. You said that you took the cabling
off and redid them, so I suspect that there is a broken audio cable, possibly between the RRC
and the K3/0 mini. The mini uses the "octopus" cable, so it would be difficult to plus into a wrong
connector somewhere, which causes a lot of problems with other rigs.
I would use an ohmmeter and make sure that the audio cable is working. There is no other explanation
beyond a wrong K3 setting, but you already checked that.
73,
Mitch DJ0QN / K7DX