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 75W into 8 ohms. That is about 1.2dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (150W and 200W). |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | evenly matched | Only SVS Prime SoundBase has AirPlay 2 and DTS Play-Fi; only WiiM Amp Ultra has Roon. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only SVS Prime SoundBase has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | B | WiiM Amp Ultra costs less - $549 against $699 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 SVS Prime SoundBase 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 is the easier recommendation: it leads on most of the measured areas and costs less. Take SVS Prime SoundBase if one of the "depends" rows above describes your system.
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.