I will do my best to give a balanced opinion on the Lumin Music Server, since obviously we carry the line. Sonically, you will either love it or find it decent. This depends on what you are after. Highly resolving DACs like the Meitner MA1, EMM Labs DAC2X, Berkeley Alpha DAC2, Bricasti M1, MSB Diamond Stack, Weiss Medus, Viola Crescendo, etc. are about resolution and detail. All have different flavors, but their goal is to reproduce sound with exquisite accuracy, holographic imaging, superb sound staging, micro transient detail and a very low noise floor. They mostly get out of the way, like a good passive preamp, and report what's on the recording. As we all know, the best recordings sound magical with these DACs. The other crap recordings that represent 80% or more of what is commercially produced sound, well, weak!
The Lumin offers a smooth, liquid sound. It is something you just listen. Music sounds great, and your mind lets go and focuses on the music, instead of the equipment. With the more detailed DACs, you are probably more likely to listen to how resolving the equipment is, and if you want to hear lesser recordings with these DACs, you may search for a tube preamp or other harmonic-producing devices to fatten and sweeten up the sound.
Using the Lumin with its own DAC, in my opinion, is like adding some tube saturation into the chain. It takes the edge off and makes digital music very listenable. If you like hyper resolution, the Lumin's on board DAC probably isn't for you. But if you like a nice sound, it's a great device. It won't outperform $10-20k DACs, obviously. But the on board DAC is quite good.
The Lumin really shines in terms of implementation. It just works out of the box, which is more than I can say for many of the other music servers we have tested. It is truly plug and play. If you are a PC user (or an adventurous Mac user willing to use the beta version), use J River Media Center. Set up a generic DLNA server, ensure that data is passed through in full resolution (via a couple of settings in J River) and select the Lumin as the output device. You can then use J Remote (the BEST iPad app for music listening/browsing in my opinion) to play the Lumin. Any format you throw at the Lumin, it will just play!
And if you still want hyper resolution for your very best recordings. use the SPDIF output to feed your hyper resolving DAC. Of course, if you have the means, the Viola Crescendo is an absolute must-listen!