These are not the same size of amplifier: Rotel Diamond RA-6000 has roughly 3.3x the power of Primare I15. That is about 5.2dB, 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 | B | Rotel Diamond RA-6000 has more power - 200W against 60W into 8 ohms. That is about 5.2dB - 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 Primare I15 the better fit for desk or near-field listening, a small room and a mid-size room, and Rotel Diamond RA-6000 for a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (100W and 350W). |
| Noise floor | B | Rotel Diamond RA-6000 is the quieter design on paper - 103dB against 97dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Rotel Diamond RA-6000 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | evenly matched | Only Rotel Diamond RA-6000 has Roon. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | A | Primare I15 takes more analogue sources - 5 against 4. |
| Phono stage | depends | Rotel Diamond RA-6000 has a built-in phono stage (MM) and Primare I15 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 Rotel Diamond RA-6000 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Primare I15 is Class D and Rotel Diamond RA-6000 is Class A/B. Class D runs cool and draws almost nothing at idle; 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 | Primare I15 takes up about 30% less shelf area (1387cm² against 1979cm²), and it is 63mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Primare I15 costs less - $1,695 against $4,500 at list. |
| Watts per dollar | B | Rotel Diamond RA-6000 is the cheaper watt - about $23 per watt against $28. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Primare I15 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?
The usual trade-off: Rotel Diamond RA-6000 measures better, Primare I15 costs about 62% less. With most speakers in most rooms that gap is smaller in practice than it looks here. 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 - Rotel Diamond RA-6000 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 60 watts is already more than most people ever use, and the extra 140 watts would be headroom you pay for and never hear - we rate Rotel Diamond RA-6000 poorly for near-field use for exactly that reason. 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.