audiophile的官網有不少可供學習的資訊
讓我節錄一段：
http://www.audiophilleo.com/en/definitions.aspx?Direct%20connection
Direct connection
...
The Audiophilleo is designed to produce the lowest jitter, and sound best,
without the use of a cable. If you already have quality S/PDIF cables, try
them out, but the sound may be even better using direct connection. Here’s
why:
With an ordinary USB-S/PDIF interface, the sound may improve with a longer,
or simply a different, cable, because of improved impedance matching and
reflection suppression. Remember that “digital” signals are just
oddly-shaped analogue wave forms; like water waves in a pool, they can reflect
off the sides and create complicated interference patterns. See
http://www.positive-feedback.com/Issue14/spdif.htm for more.
And, as a general rule, any device driving a short cable must have very fast
rise-times or “edges” to avoid jitter created by interfering internal
electrical reflections. The relatively slow, 25 ns transitions typical of
many USB-S/PDIF devices are more compatible with longer cables, which in turn
reduces these reflections and their contribution to clock jitter.
...
結論：除非耳朵收貨，不然一般的DDC還是乖乖上條線吧。
題外話，這種根據理論實作的風格真對我胃口，坐等原PO開團XDD