These are not the same size of amplifier: HiFi Rose RS520 has roughly 6.3x the power of Naim Uniti Atom. That is about 8dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | A | HiFi Rose RS520 has more power - 250W against 40W into 8 ohms. That is about 8dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Room size | depends | We rate HiFi Rose RS520 the better fit for a large room and a very large room, and Naim Uniti Atom for desk or near-field listening, a small room and a mid-size room. Match the amplifier to the room you actually have, not the one you want. |
| Built-in DAC | A | Both decode on board. HiFi Rose RS520 goes higher - 768kHz against 384kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | evenly matched | Only Naim Uniti Atom has Chromecast. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only Naim Uniti Atom has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | HiFi Rose RS520 is Class AD and Naim Uniti Atom is Class A/B. Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Naim Uniti Atom takes up about 31% less shelf area (781cm² against 1135cm²). |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | A | HiFi Rose RS520 is the cheaper watt - about $15 per watt against $95. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A HiFi Rose RS520 B Naim Uniti Atom
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?
HiFi Rose RS520 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 - HiFi Rose RS520 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 40 watts is already more than most people ever use, and the extra 210 watts would be headroom you pay for and never hear - we rate HiFi Rose RS520 poorly for near-field use for exactly that reason.
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.