These are not the same size of amplifier: Yamaha A-S501 has roughly 2.8x the power of OSD Nero Stream XD. That is about 4.5dB, 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 | B | Yamaha A-S501 has more power - 85W against 30W into 8 ohms. That is about 4.5dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate OSD Nero Stream XD the better fit for desk or near-field listening and a small room, and Yamaha A-S501 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. |
| Noise floor | B | Yamaha A-S501 is the quieter design on paper - 99dB against 95dB. 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. |
| Analogue inputs | B | Yamaha A-S501 takes more analogue sources - 6 against 1. |
| Phono stage | depends | Yamaha A-S501 has a built-in phono stage (MM) and OSD Nero Stream XD 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. |
| Amplifier class | depends | OSD Nero Stream XD is Class D and Yamaha A-S501 is Class A/B. Class D runs cool and draws almost nothing at idle; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | OSD Nero Stream XD takes up about 78% less shelf area (384cm² against 1710cm²), and it is 194mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | OSD Nero Stream XD costs less - $240 against $550 at list. |
A OSD Nero Stream XD B Yamaha A-S501
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: Yamaha A-S501 measures better, OSD Nero Stream XD costs about 56% 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 - Yamaha A-S501 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 30 watts is already more than most people ever use, and the extra 55 watts would be headroom you pay for and never hear - we rate Yamaha A-S501 poorly for near-field use for exactly that reason. If you play records, Yamaha A-S501 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.