These are not the same size of amplifier: NAD C 399 has roughly 2.6x the power of Technics SU-G700M2 Grand Class. That is about 4.1dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | A | NAD C 399 has more power - 180W against 70W into 8 ohms. That is about 4.1dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate NAD C 399 the better fit for a large room and a very large room, and Technics SU-G700M2 Grand Class for desk or near-field listening, a small room and a mid-size room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | B | Technics SU-G700M2 Grand Class holds up better into a 4-ohm load: its output nearly doubles to 140W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Analogue inputs | evenly matched | The same number of line-level inputs (2). |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | B | Technics SU-G700M2 Grand Class costs less - $2,700 against $2,899 at list. |
| Watts per dollar | A | NAD C 399 is the cheaper watt - about $16 per watt against $39. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A NAD C 399 B Technics SU-G700M2 Grand Class
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?
The usual trade-off: NAD C 399 measures better, Technics SU-G700M2 Grand Class costs about 7% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Technics SU-G700M2 Grand Class 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 399 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 70 watts is already more than most people ever use, and the extra 110 watts would be headroom you pay for and never hear - we rate NAD C 399 poorly for near-field use for exactly that reason.
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.