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 | evenly matched | Effectively the same output - 55W against 55W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (105W and 105W). |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | A | Only Yamaha WXA-70A has AirPlay 2, Chromecast, Roon and Qobuz. |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Use with a TV | depends | Only Yamaha WXA-70A has HDMI eARC/ARC, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | B | Yamaha WXA-50 costs less - $599 against $1,300 at list. |
| Watts per dollar | B | Yamaha WXA-50 is the cheaper watt - about $11 per watt against $24. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Yamaha WXA-70A B Yamaha WXA-50
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 this sits under a television, Yamaha WXA-70A is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way. 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.