NAD M51 vs C510


I'm having a hard time understanding something - I'm shopping around for a new DAC, and the NAD M51 comes highly rated. About a year ago, NAD released the C510 with identical specs. However, it's $500 cheaper than the M51 with the difference being the M51 boasts a better power supply. I asked the sales rep what that means in the real world, and he literally said "I couldn't tell you." So if the 2 units have literally identical data sheets, what does one get with an improved PSU? Specs below, from the service manual for each unit:

M51:

Rated distortion (THD+N with AES 17 flter) <0.0005% (ref. 1 kHz 0 dBFS)
<0.002% (ref. 1 kHz -60 dBFS)
IM distortion <0.0001%
Signal-to-noise ratio < -123 dB (ref. 0 dBFS 2V out)
Channel separation > -115 dB (ref. 0 dBFS Volume -1dB)
Sample rate 32 kHz to 192 kHz (USB and digital S/PDIF)
Frequency response ±0.5 dB (ref. 20 Hz – 96 kHz @ 192 KHz sample rate)
Output level 2V (ref. input 0dBFS)

C510:

Rated distortion (THD+N with AES 17 flter) <0.0005% (0dBFS)
<0.002% (-60dBFS)
IMD Distortion 0.0001%
Signal/Noise Ratio <-123dB (ref. 0dBFS 2V out)
Channel Separation >-115dB (ref. 0dBFS Volume -1dB)
Sample Rate 32kHz to 192kHz (USB and digital S/PDIF)
Frequency Response ±0.5dB (ref. 20Hz - 96kHz @ 192kHz sample rate)
Output Level 2V (ref. input 0dBFS)
caustic386
From what I read, the differentiation seems to be about features and utility, with the M51 being more of a dedicated DAC and the C510 a DAC/"Digital preamp." Connectivity seems to be the same in both cases. Hypothetically, a better power supply might provide more dynamic headroom in the analog output section, but best compared directly in listening. Power supplies are the most expensive part of any component. Hopefully, others here will chime in with direct experience. But NAD is a good choice all around.
Would more headroom assist at lower volumes if properly implemented?  Hypothetically of course - I agree firsthand listening is the only way to know.   I'm also currently demo'ing a Benchmark DAC2 which is absolutely excellent at lower volumes (important distinction when you have a newborn in the house).

I took a look. These appear to be very similar. The audio output stage and power supply sections appear to be exactly the same, hence the same specs. However, the center section of the board on the M51 is more densely populated and appears to have a smaller DSP or IC in the digital receiver area.

M51:

http://d250ptlkmugbjz.cloudfront.net/info/IMG/jpg/Interieur-15.jpg


C510:

http://www.hifisentralen.no/forumet/attachments/hi-fi-generelt/287297d1415136705-nad-c510-p1020896.jpg

It seems, like stevecham said, it’s a slightly different feature set. IF the C510 operates like a digital preamp, there’s some additional processing on the bitstream data to make this happen.

Interesting idea - I never would've thought to look at the internals, mainly because I have no idea what I'm looking at.  Thinking through both poster's points about Digital Pre vs. DAC - they seem to have the same feature set.  Same # of inputs, outputs, etc. - no room correction, effects or anything like that.  With that in mind, what constitutes one as a pre vs simply a DAC (marketing aside)?

"High end" audio is so confusing...