USB Host shield Sparkfun

Does anyone know what pin the USB host shield uses as a transmitter? I'm trying to stack a DK Electronics motor shield on top of it, however, it's not working even with the supplied 12V.

So I'm starting to think that my shields are not pin compatible, and that both shields use the same pins for transmitting data.

For an SPI input you want all the shields to have the same "transmitter", what you want is different chip selects. Is that what you are asking?