I have a Sound Devices MixPre D and I wanted to use it to record something on my Mac. I plugged it in and went to the midi control panel and changed the input and output to the Mixpre-D which showed up in the menu there.
The thing is, with my other input options, like my webcam, there is also the ability to adjust the input volume. Not for the Mixpre-D though.
The result is that if I set my levels correctly on the Mixpre-D , the input level coming into my Mac is VERY low. I recorded a screen captured video and in Final Cut had to apply the max +12 gain to the audio track and that still didn't get me in quite the right place!
I tried in Garageband as well and the there is only the smallest almost imperceptible movement on the mic level meter there as well.
Contact Sound Devices and then report back. I didn't have any problems when I reviewed it last year. The USB output of the MixPre D is digital, so if you're getting good levels into it, it doesn't make sense that they are showing up low in your Mac.