I own the Simaudio 100D, the little brother of the 300D, and it's a wonderful, natural sounding DAC.
If your primary source will be USB, though, the 300D is probably not the best choice. Simaudio makes it very clear in their description of both the 100D and the 300D that they put their effort into the SPDIF circuits and include the USB input mostly as a convenience.
If your primary source will be USB, though, the 300D is probably not the best choice. Simaudio makes it very clear in their description of both the 100D and the 300D that they put their effort into the SPDIF circuits and include the USB input mostly as a convenience.