I bought one of the Topping D3 DACs from the UK importer a couple of months ago, and I am delighted with it.
I bought it specifically to use with the optical output from my Cocktail Audio X10 (because the internal audio amp is lousy) and it is excellent. The sound is sweet and pure and stereo imagery is excellent with nice tight bass. I'm feeding it into my Marantz stereo amp and also to my top end Senheiser headphones.
For the price this is an excellent product. I would buy again if I needed to replace it