You might get 24/48 audio (which is what most blurays are produced at), but it will be 2-channel stereo. This is most likely the 2-channel stereo audio track on the bluray that can be used for Dolby Pro Logic surround decoding. Multi-channel audio cannot be sent across USB. Per licensing, only HDMI can send multi-channel DTS-HD or TrueHD.
Even if the computer did send some form the DTS signal, the USB DAC would not be able to decode it.