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 | A | WiiM Amp Ultra has more power - 100W against 55W into 8 ohms. That is about 2.6dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (200W and 105W). |
| Built-in DAC | B | Both decode on board, but only Yamaha WXA-50 handles DSD. |
| Streaming | A | Only WiiM Amp Ultra has Chromecast and Roon. |
| Use with a TV | depends | Only WiiM Amp Ultra has HDMI 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 | A | WiiM Amp Ultra costs less - $549 against $599 at list. |
| Watts per dollar | A | WiiM Amp Ultra is the cheaper watt - about $5 per watt against $11. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A WiiM Amp Ultra 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?
WiiM Amp Ultra 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 - WiiM Amp Ultra has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 55 watts is already more than most people ever use, and the extra 45 watts would be headroom you pay for and never hear. If this sits under a television, WiiM Amp Ultra is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way.
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.