One is a streaming all-in-one and the other is an amplifier. Judge them on how many boxes you want and what you already own, not on the spec sheet alone.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 180W against 200W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Anthem STR holds up better into a 4-ohm load: its output nearly doubles to 400W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | B | Anthem STR is the quieter design on paper - 120dB against 110dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | Both decode on board. Arcam SA45 goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | A | Only Arcam SA45 has AirPlay 2, Chromecast and Roon. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Arcam SA45 is Class G and Anthem STR is Class A/B. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; 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. |
| Price | B | Anthem STR costs less - $5,000 against $5,500 at list. |
A Arcam SA45 B Anthem STR
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. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Anthem STR is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating.
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.