Most people here are not aware of this product. I bought a similar form Ebay as well, There are 2 versions CM6631 and CM6631A, the latter is more expensive, I bought the former it is very good, I run it into coaxial SPDIF input from my DAC.
It sounds really good better than my USB input from my DAC, really well worth the money. The CM6631 I bought comes in a box hence you don't to buy a separate box to house in it.
My next project will be to get a DAC(AK4396), CM6631(without housing) and tube buffer all house in the same box. This combo acts as DAC as well as a preamplifier output. This combo will sound very good and also very cheap less than $150.