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 - 300W against 250W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | A | Cambridge Audio Evo 300 holds up better into a 4-ohm load: its output nearly doubles to 550W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Built-in DAC | B | Both decode on board, but only HiFi Rose RS520 handles MQA. |
| Streaming | A | Only Cambridge Audio Evo 300 has AirPlay 2 and Chromecast. |
| Phono stage | depends | Cambridge Audio Evo 300 has a built-in phono stage (MM) and HiFi Rose RS520 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. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only Cambridge Audio Evo 300 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Cambridge Audio Evo 300 is Class D and HiFi Rose RS520 is Class AD. Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | HiFi Rose RS520 takes up about 22% less shelf area (1135cm² against 1463cm²), and it is 48mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | HiFi Rose RS520 costs less - $3,695 against $3,999 at list. |
A Cambridge Audio Evo 300 B HiFi Rose RS520
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?
The usual trade-off: Cambridge Audio Evo 300 measures better, HiFi Rose RS520 costs about 8% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Cambridge Audio Evo 300 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you play records, Cambridge Audio Evo 300 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.