Can I use my Android phone as a USB speaker?
Even though I marked this as answered I feel I need to add that I've managed to do exactly what I wanted with SoundWire and the default internet sharing on my phone as follows:


Install and configure SoundWire on PC and phone.
Share phone's internet connection via USB.
Assuming you already had internet on your PC, you now have 2 network adapters. You need to make sure you are using your old adapter for internet access. As far as I could find to do this you need to change the metric of your default adapter to 1 so that it is the preferred adapter by Windows (Windows 7 in my case).
You can check the server IP by typing ipconfig in the command prompt.
Connect from the SoundWire app on your phone. You get a message that WiFi is disabled, but it still works fine.