I bought the D03K to connect the optical audio output from an Apple TV to the analogue stereo inputs of my TV sound system. It was bought on the strength of various web reviews and I have to say I've not been disappointed so far.
I need to say her...Read moree that I don't pretend to be an audiophile but the sound quality from my system using the D03K DAC to play back lossless AAC music files from iTunes is no different to my ears than the Airport Express (current version) I used previously. Comparing the sound via the D03K to the same tracks played from my Sony DVD/CD player also reveals no difference in sound quality. The D03K output level is slightly lower (1.5V) than the Airport Express (2.0V), however, which means the volume has to be turned up a little higher. It is not that much different in sound level to my Humax satellite box output, though.
The D03K is so small I was able to conceal it behind one of the connector covers on the back of my TV, making it invisible aside from the cables. That is probably not a concern for most buyers but it is for me as I'm a bit of a fanatic about tidy cabling and trailing sockets! The connectors are also very secure so little risk of a cable dropping out.
I had hoped to power the D03K from a USB port on my satellite box so that it would switch on and off with the TV. However, I found that this introduced some grounding hum (only noticeable at high volumes between music tracks and probably not an issue for TV only operation). I now have it connected direct to a USB wall plug, which has eliminated the problem but means it is always powered on. Time will tell if this results in a shortened lifetime. Hopefully not but then its not the world's most expensive DAC so buying another is always an option!
In summary, the D03K is doing exactly what I had hoped in terms of allowing me to connect an optical source to an analogue sound systems. The sound quality is excellent and the price from Advanced MP3 Players one fifth that of the alternative 'hifi' solution I had considered. Hopefully, it will proved a durable solution, too.