RAKK DAC is a kit (you can also buy a completed version) available from K&K Audio. This unit uses the TI/Burr-Brown PCM1794 DAC coupled with the CS4816 input receiver . I'm currently running the first 'MK 1' iteration that does not have upsampling.
What drew me to this DAC was the novel I/V converter - it does not use an op-amp, tubes, resistor or a mess of transistors - but instead a Lundahl LL1674 1:4 step-up amorphous core transformer. This should provide 'galvanic isolation' from higher frequency digital crud and buffer the PCM1794 from seeing any outside world nasties. This 'transformer' only output is known as the 'Passive Output Stage' and it does suffer from a high output impedance of ~3000 ohms. K&K also offers a lower impedance active output stage using 6N6Ps and Lundahl iron.
A power supply board is also needed - along with RCA jacks, PCB standoffs, wire and of course a bit of solder to hold everything together. I ended up using Vampire RCA jacks and some 21awg solid-core silver wire I bought from Michael Percy.
I stuck the boards and transformers inside of an old Video Generator chassis that already had an IEC plug, fuse and holes for mounting RCA jacks. It sure doesn't look pretty but my DAC budget was already blown by the time I was done buying all the parts from K&K.
How does it sound? It took awhile for the transformers to break in since the treble was initially very edgy and forward sounding. After a few hours, the sound began to settle down. This certainly is some of the best digital I have heard - smooth treble with a fast but surprisingly musical quality. Definition and detail is excellent for Redbook playback, with plenty of appropriate reverb and hall sound coming through. Dynamics are big and lesser DACs sound compressed in comparison. I'm reminded of a good turntable setup - the overall sound certainly doesn't drive me out of the room like some budget CD or DVD players do.
Compared to the Monica 2 DAC, the RAKK is more neutral and has more detail. The Monica is certainly warm and forgiving, but has a thicker sound with a rolled off treble. However the Monica excels at removing the digital nasties from poorer recordings. The RAKK can be more ruthless in comparison.
Compared to the budget Sony SCD-CE595 SACD player, the RAKK has a smoother treble and is more musical sounding overall. That probably has much to do with the 595's op-amp output stage. I'm afraid to say that even SACD discs on the Sony suffer in comparison. The 595 does however slightly outpace the RAKK on information retrieval - but such is the nature of hi-rez digital versus the older redbook technology.
The RAKK has been the only mainstay of my system for the past two years. Someday I'll upgrade or replace it, but for now it continues to satisfy my digital playback needs.