Which DAC as a preamp?

Hi folks...I am looking for opinions regarding DACs to use as a digital pre-amp to drive my red dragon monoblocks. I am considering Audiolab MDAC plus, Musical Fidelity M6s DAC, NAD C-510, or the Audio Alchemy DDP-1.    Any thoughts as to which would be the best pick?
From someone who’s actually been designing preamp/amps for almost half a century instead of just reading the specs. 


Thanks for all the input folks. I ended up with a good deal on a nice peach tree sonadac. Small form factor like the amps...triggers them by remote....running balanced cables...sounds great. I am breaking the amps in, but so far I am VERY impressed with the red dragon amps as well. This may be my favorite system of all time!
Have had the DDP-1 and the M6S. The latter blows most DACs (from Ayre, PS Audio, Chord) out of the water in terms of retrieving ambient cues and resolution of depth. It is dynamic, tremendously low in noise and listening fatigue, tonally balanced (if a smidge cooler than the Audio Alchemy), and genuinely believable, in a way few components ever are, I think there’s something special about this iteration of Musical Fidelity’s DAC. I have not tried the earlier ones but understand they’re not quite this special. I’m keeping it alongside my Lampizator; it’s that good. I keep coming back to that cathedral like soundstage and realism. 
Cary 600.  Friggin awesome as a stand-alone with a 3 volt outputDoes it all and sounds fantastic.   Based on AKM 4497 Dac set. 28 lb beast. All sorts of digital ins and outs. Roon , Mqa, integrated SD card reader. It is sweet  and you will never tire of listening to it