I'm puzzled: how is the slave selected by wiringPiSPIDataRW()? I presume you have to set the slave pin low yourself, although I have NEVER seen any example of where this is done.
I notice on the pinout that there is a CE0 and CE1 for both SPI0 and SPI1. Is that what you use for the "channel" parameter in wiringPiSPIDataRW()? If so, it's very ambiguous, as wiringPiSPISetup() also has a channel parameter.
Does that also mean that each wiringPi "channel" can only select two slaves?