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 | A | HiFi Rose RS520 has more power - 250W against 200W into 8 ohms. That is about 1dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | B | Rotel Diamond RA-6000 holds up better into a 4-ohm load: its output increases strongly to 350W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | HiFi Rose RS520 is the quieter design on paper - 109dB against 103dB. Audible mainly with sensitive speakers in a quiet room. |
| 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 | The same streaming platforms and services on both. |
| Analogue inputs | B | Rotel Diamond RA-6000 takes more analogue sources - 4 against 1. |
| Phono stage | depends | Rotel Diamond RA-6000 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 | B | Only Rotel Diamond RA-6000 offers A/B speaker terminals - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Headphones | depends | Only Rotel Diamond RA-6000 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 Rotel Diamond RA-6000 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 | HiFi Rose RS520 takes up about 43% less shelf area (1135cm² against 1979cm²), and it is 128mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | HiFi Rose RS520 costs less - $3,695 against $4,500 at list. |
| Watts per dollar | A | HiFi Rose RS520 is the cheaper watt - about $15 per watt against $23. 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 Rotel Diamond RA-6000
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. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Rotel Diamond RA-6000 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you play records, Rotel Diamond RA-6000 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.