These are not the same size of amplifier: Technics SU-G700M2 Grand Class has roughly 2.3x the power of Technics SU-GX70. That is about 3.7dB, 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 | Technics SU-G700M2 Grand Class has more power - 70W against 30W into 8 ohms. That is about 3.7dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Technics SU-G700M2 Grand Class the better fit for a mid-size room, a large room and a very large room, and Technics SU-GX70 for desk or near-field listening and a small room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (140W and 60W). |
| Built-in DAC | A | Both decode on board. Technics SU-G700M2 Grand Class goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | B | Only Technics SU-GX70 has AirPlay 2 and Chromecast. |
| Analogue inputs | evenly matched | The same number of line-level inputs (2). |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Technics SU-GX70 takes up about 17% less shelf area (1711cm² against 2069cm²), and it is 83mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Technics SU-GX70 costs less - $1,999 against $2,700 at list. |
| Watts per dollar | A | Technics SU-G700M2 Grand Class is the cheaper watt - about $39 per watt against $67. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Technics SU-G700M2 Grand Class B Technics SU-GX70
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: Technics SU-G700M2 Grand Class measures better, Technics SU-GX70 costs about 26% less. With most speakers in most rooms that gap is smaller in practice than it looks here. 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 - Technics SU-G700M2 Grand Class has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 30 watts is already more than most people ever use, and the extra 40 watts would be headroom you pay for and never hear - we rate Technics SU-G700M2 Grand Class poorly for near-field use for exactly that reason. Think about the whole system: the roughly $701 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.