That would bypass your soundcard's dac yes. Thing is, your soundcard may not output surround or other features to the optical out, making it effectively something you won't need as your own dac already does stereo in the same manner. I assume you want virtual surround? If not, just use your Benchmark dac through usb, though perhaps the Benchmark dac may do better through optical than usb which may be why it sounds better for you. Either way, the signal is digital and only processed by the DAC you own, not the soundcard.