These are not the same size of amplifier: Rotel Diamond RA-6000 has roughly 2.5x the power of Rotel S14. That is about 4dB, 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 80W into 8 ohms. That is about 4dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Rotel S14 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 nearly doubles (150W and 350W). |
| Noise floor | B | Rotel Diamond RA-6000 is the quieter design on paper - 103dB against 100dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | A | Only Rotel S14 has AirPlay 2 and Chromecast. |
| 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 Rotel S14 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. |
| Shelf space | depends | Rotel S14 takes up about 18% less shelf area (1629cm² against 1979cm²), and it is 79mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Rotel S14 costs less - $2,499 against $4,500 at list. |
| Watts per dollar | B | Rotel Diamond RA-6000 is the cheaper watt - about $23 per watt against $31. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rotel S14 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, Rotel S14 costs about 44% 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, 80 watts is already more than most people ever use, and the extra 120 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.