These are not the same size of amplifier: Denon DRA-900H has roughly 2x the power of Audiolab 6000A. That is about 3dB, 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 | Denon DRA-900H has more power - 100W against 50W into 8 ohms. That is about 3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Built-in DAC | A | Both decode on board, but only Denon DRA-900H handles DSD. |
| Streaming | A | Only Denon DRA-900H has AirPlay 2 and HEOS. |
| Analogue inputs | B | Audiolab 6000A takes more analogue sources - 4 against 2. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | A | Denon DRA-900H costs less - $799 against $899 at list. |
| Watts per dollar | A | Denon DRA-900H is the cheaper watt - about $8 per watt against $18. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Denon DRA-900H B Audiolab 6000A
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?
Denon DRA-900H is the easier recommendation: it leads on most of the measured areas and costs less. Take Audiolab 6000A if one of the "depends" rows above describes your system. 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 - Denon DRA-900H has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 50 watts is already more than most people ever use, and the extra 50 watts would be headroom you pay for and never hear.
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.