No single best amplifier here. What decides it is what you have to drive, what you need to plug in, and how much of the system you want in one box.
| Area | Better | Why |
|---|
| Power | A | Emotiva BasX A2+ has more power - 160W against 100W into 8 ohms. That is about 2dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Emotiva BasX A2+ the better fit for a very large room, and Yamaha A-S701 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. |
| Bass control | A | Emotiva BasX A2+ has the higher damping factor (500 vs 240), which usually means a tighter grip on a woofer. Above about 100 the returns flatten out, so read this as a tendency rather than a ranking. |
| Noise floor | A | Emotiva BasX A2+ is the quieter design on paper - 112dB against 99dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Yamaha A-S701 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Yamaha A-S701 takes more analogue sources - 6 against 2. |
| Phono stage | depends | Yamaha A-S701 has a built-in phono stage (MM) and Emotiva BasX A2+ does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Headphones | depends | Only Yamaha A-S701 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | A | Emotiva BasX A2+ is the cheaper watt - about $5 per watt against $8. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Emotiva BasX A2+ B Yamaha A-S701
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?
Emotiva BasX A2+ has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. 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 - Emotiva BasX A2+ has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 100 watts is already more than most people ever use, and the extra 60 watts would be headroom you pay for and never hear - we rate Emotiva BasX A2+ poorly for near-field use for exactly that reason. If you play records, Yamaha A-S701 saves you buying a phono stage; if you do not, ignore that row entirely.
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.