These are not the same size of amplifier: Rega Osiris has roughly 2.2x the power of Rega Elex Mk4. That is about 3.5dB, 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 | Rega Osiris has more power - 160W against 72W into 8 ohms. That is about 3.5dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Rega Osiris the better fit for a large room and a very large room, and Rega Elex Mk4 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 | B | Rega Elex Mk4 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | evenly matched | The same number of line-level inputs (5). |
| Phono stage | depends | Rega Elex Mk4 has a built-in phono stage (MM) and Rega Osiris 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. |
| Headphones | depends | Only Rega Elex Mk4 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | B | Rega Elex Mk4 costs less - $1,895 against $11,600 at list. |
| Watts per dollar | B | Rega Elex Mk4 is the cheaper watt - about $26 per watt against $73. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rega Osiris B Rega Elex Mk4
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?
Rega Elex Mk4 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 - Rega Osiris has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 72 watts is already more than most people ever use, and the extra 88 watts would be headroom you pay for and never hear - we rate Rega Osiris poorly for near-field use for exactly that reason. If you play records, Rega Elex Mk4 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.