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 | B | Marantz Model 40n has more power - 70W against 50W into 8 ohms. That is about 1.5dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Audiolab Omnia the better fit for desk or near-field listening and a small room, and Marantz Model 40n for a mid-size room, 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 modestly (75W and 100W). |
| Noise floor | B | Marantz Model 40n is the quieter design on paper - 106dB against 76dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | Both decode on board. Audiolab Omnia goes higher - 768kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | evenly matched | Only Audiolab Omnia has DTS Play-Fi; only Marantz Model 40n has AirPlay 2 and HEOS. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | A | Audiolab Omnia takes more analogue sources - 4 against 3. |
| Room to grow | A | Only Audiolab Omnia offers a pre-out/main-in loop - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Built-in sources | depends | Audiolab Omnia has a CD player built in. That is one less box if you still play discs or listen to radio, and dead weight if you do not. |
| Shelf space | depends | Audiolab Omnia takes up about 26% less shelf area (1582cm² against 2126cm²), and it is 123mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Audiolab Omnia costs less - $2,300 against $2,499 at list. |
| Watts per dollar | B | Marantz Model 40n is the cheaper watt - about $36 per watt against $46. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Audiolab Omnia B Marantz Model 40n
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it.
What a spec sheet cannot show: how either sounds with your speakers, how the interface feels 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.