These are not the same size of amplifier: FiiO AIR AMP has roughly 3x the power of OSD Nero Stream XD. That is about 4.8dB, 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 | FiiO AIR AMP has more power - 90W against 30W into 8 ohms. That is about 4.8dB, 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 FiiO AIR AMP 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 | A | OSD Nero Stream XD holds up better into a 4-ohm load: its output increases strongly to 50W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Built-in DAC | B | Both decode on board. FiiO AIR AMP goes higher - 768kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | evenly matched | Only FiiO AIR AMP has Roon. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only OSD Nero Stream XD has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | A | OSD Nero Stream XD costs less - $240 against $300 at list. |
| Watts per dollar | B | FiiO AIR AMP is the cheaper watt - about $3 per watt against $8. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A OSD Nero Stream XD B FiiO AIR AMP
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: FiiO AIR AMP measures better, OSD Nero Stream XD costs about 20% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - OSD Nero Stream XD is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. 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 - FiiO AIR AMP 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 60 watts would be headroom you pay for and never hear - we rate FiiO AIR AMP poorly for near-field use for exactly that reason.
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.