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USB Audio and Mac OS X

We develop an USB audio device. It works perfectly with Windows XP and I meet a problem with Mac OS. It seems that mixer unit are not managed by Mac OS X usb audio implementation.
Under Windows XP Line monitoring and output feature units are accesible using control panel. Under Mac OS X only the output feature unit is accessible.

Here are the descriptors

//---------------- For LineIn monitoring ------------
// Input Terminal Descriptor
0x0C,     // bLength
0x24,     // bDescriptorType
0x02,     // bDescriptorSubtype
DEV_LINEMON_IT_ID,     // bTerminalID
0x03, 0x06,     // wTerminalType, line connector in
0x00,     // bAssocTerminal
0x02,     // bNrChannels
0x03, 0x00,     // wChannelConfig
0x00,    
0x00,

// Feature Unit
0x09,     // bLength
0x24,     // bDescriptorType
0x06,     // bDescriptorSubtype
DEV_LINEMON_FU_ID,     // bUnitId
DEV_LINEMON_IT_ID,     // bSourceId
0x01,     // bControlSize
0x01,     // master mute
0x00,     // channel 1
0x00,    

//---------------- For LineIn ------------
// Input Terminal Descriptor
0x0C,     // bLength
0x24,     // bDescriptorType
0x02,     // bDescriptorSubtype
DEV_LINEREC_IT_ID,     // bTerminalID
0x03, 0x06,     // wTerminalType, line connector in
0x00,     // bAssocTerminal
0x02,     // bNrChannels
0x03, 0x00,     // wChannelConfig
0x00,     
0x00,

// Output Terminal Descriptor
0x09,     // bLength
0x24,     // bDescriptorType
0x03,     // bDescriptorSubtype
DEV_LINEREC_OT_ID,     // bTerminalID
0x01, 0x01,     // wTerminalType
0x00,     // bAssocTerminal
DEV_LINEREC_IT_ID,    
0x00,

//-------- For Host USB audio stream out -----
// Input Terminal Descriptor  
 0x0C,     // bLength
0x24,     // bDescriptorType
0x02,     // bDescriptorSubtype
DEV_HOST_IT_ID,     // bTerminalID
0x01, 0x01,     // wTerminalType USB stream
0x00,     // bAssocTerminal
0x02,     // bNrChannels
0x03, 0x00,     // wChannelConfig
0x00,    
0x00,    

//---------------- For Mixer ------------------
// Mixer Unit Descriptor
0x0E,     // bLength
0x24,     // bDescriptorType
0x04,     // bDescriptorSubtype
DEV_SPK_MIXER_ID,     // bTerminalID
0x02,     // 2 input pins
DEV_LINEMON_FU_ID,     // second input is from Line in
DEV_HOST_IT_ID,     // first input is from Speaker
0x02,     // Two logical channel output
0x03, 0x00,     // stereo left/right
0x00,
0x00, 0x00,
0x00,    

//---------------- For Speaker Ouput ----------
// Feature Unit
0x0A,     // bLength
0x24,     // bDescriptorType
0x06,     // bDescriptorSubtype
DEV_SPK_FU_ID,     // bUnitId
DEV_SPK_MIXER_ID,     // bSourceId
0x01,     // bControlSize
0x01,     // master mute
0x02,     // channel 1 volume
0x02,     // channel 2 volume
0x00,

// Output Terminal Descriptor
0x09,     // bLength
0x24,     // bDescriptorType
0x03,     // bDescriptorSubtype
DEV_SPK_OT_ID,     // bTerminalID
0x01, 0x03,     // wTerminalType, generic speaker
0x00,     // bAssocTerminal
DEV_SPK_FU_ID,    
0x00,     
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