One is a streaming all-in-one and the other is an amplifier. Judge them on how many boxes you want and what you already own, not on the spec sheet alone.
| Area | Better | Why |
|---|
| Power | B | NAD C 379 BluOS-D has more power - 80W against 50W into 8 ohms. That is about 2dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Grip on hard loads | A | Audiolab 6000A MKII holds up better into a 4-ohm load: its output increases strongly to 75W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Audiolab 6000A MKII is the quieter design on paper - 110dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board. NAD C 379 BluOS-D goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | B | Only NAD C 379 BluOS-D has AirPlay 2, Roon and BluOS. |
| Room to grow | A | Only Audiolab 6000A MKII offers a pre-out/main-in loop - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | Audiolab 6000A MKII is Class A/B and NAD C 379 BluOS-D is Class D. Class A/B runs warm and is the long-established mainstream choice; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Audiolab 6000A MKII takes up about 27% less shelf area (1328cm² against 1810cm²), and it is 117mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Audiolab 6000A MKII costs less - $1,099 against $1,499 at list. |
A Audiolab 6000A MKII B NAD C 379 BluOS-D
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both amplifiers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Audiolab 6000A MKII is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - NAD C 379 BluOS-D has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 50 watts is already more than most people ever use, and the extra 30 watts would be headroom you pay for and never hear.
What a spec sheet cannot show: how either sounds with your speakers, how the controls feel day to day, and what the app is like to live with - which is where most all-in-one amplifiers are actually won or lost. Power figures are the manufacturers' own and are not measured to a common standard, so treat small differences as noise. If you can hear both, that will tell you more than any row above.