USB to SPDIF
Although it’s quickly changing, the audio world hasn’t been very computer minded. Up until about a year or so ago, most hifi gear only had provisions for a digital connection in the form of SPDIF. However, all PCs have a USB port but only a handful (most of which are multimedia models) have an SPDIF out. So, if you wish to connect a PC without an SPDIF to hifi gear with SPDIF input only, an asynchronous USB to SPDIF converter is the solution. Moreover, a 24/192 USB-to-SPDIF converter is also a useful upgrade if you have an older dac that is limited to 24/96 on it’s USB input.
Berkeley

The Alpha USB
The Alpha USB is an asynchronous High Speed USB to digital audio interface that extracts the highest possible audio quality from computer audio sources. Read More
Musical Fidelity

V-LINK192 – USB/SPDIF Conv.
The V-LINK192 is a USB converter capable of transfering the very highest resolution music files.
Wavelength

WaveLink HS 24/192 USB to SPDIF Converter
While this will not bring legacy DACS up to the asynchronous capabilities of direct USB connectivity it will do a lot for those people wanting to connect their SPDIF dacs to computers. Read More