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 | B | WiiM Amp Ultra has more power - 100W against 70W into 8 ohms. That is about 1.5dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | B | WiiM Amp Ultra holds up better into a 4-ohm load: its output nearly doubles to 200W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Price | B | WiiM Amp Ultra costs less - $549 against $599 at list. |
| Watts per dollar | B | WiiM Amp Ultra is the cheaper watt - about $5 per watt against $9. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Cambridge Audio MXW70 B WiiM Amp Ultra
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. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - WiiM Amp Ultra is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating.
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.