To be more precise, I think we need:
The following constants regarding "request" numbers of usb which are used to communicate with the interface. Mixer is the request for volume data. Reg1/2 are requests for special commands like switching 48V on/off and other modes. Each request again has a number for the specific data type. Those values are also important. E.g. which number has to be used to send the data in the request mixer to define the routing volume from input 1 to output 1.
These are the values for Babyface Pro from the kernel patch.
#define SND_BBFPRO_USBREQ_CTL_REG1 0x10
#define SND_BBFPRO_USBREQ_CTL_REG2 0x17
#define SND_BBFPRO_USBREQ_MIXER 0x12
OSCAR for Android and iOS with TotalMixFX templates: http://www.oscar-app.de