Yep, the BASS_DEVICEINFO "driver" member is currently unused on OSX. But here's an update to try, which will put the device's UID (unique identifier) in there... www.un4seen.com/stuff/libbass.dylib
The UID can be used to get related devices via the AudioHardware API, eg. AudioObjectGetPropertyData. You would use the kAudioHardwarePropertyDeviceForUID property to translate the UID to an AudioDeviceID, and then use the kAudioDevicePropertyRelatedDevices property on that to get the related devices.