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 | evenly matched | Effectively the same output - 90W against 100W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Luxman L-505Z holds up better into a 4-ohm load: its output increases strongly to 150W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Analogue inputs | evenly matched | The same number of line-level inputs (5). |
| Phono stage | depends | Luxman L-505Z has a built-in phono stage (MM and MC) and Accuphase E-280 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. |
| Price | evenly matched | Priced within a few per cent of each other. |
A Accuphase E-280 B Luxman L-505Z
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?
Luxman L-505Z has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Luxman L-505Z is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you play records, Luxman L-505Z 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.