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 | B | AudioControl Rialto 600 has more power - 100W against 80W into 8 ohms. That is about 1dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Arcam A15 the better fit for a small room, and AudioControl Rialto 600 for 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 | B | AudioControl Rialto 600 holds up better into a 4-ohm load: its output nearly doubles to 200W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Arcam A15 is the quieter design on paper - 106dB against 96dB. 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 | A | Arcam A15 takes more analogue sources - 3 against 1. |
| Phono stage | depends | Arcam A15 has a built-in phono stage (MM) and AudioControl Rialto 600 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 | B | Only AudioControl Rialto 600 offers a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | Arcam A15 is Class A/B and AudioControl Rialto 600 is Class D. Class A/B runs warm and is the long-established mainstream choice; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | AudioControl Rialto 600 takes up about 74% less shelf area (410cm² against 1580cm²), and it is 176mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | AudioControl Rialto 600 costs less - $899 against $999 at list. |
| Watts per dollar | B | AudioControl Rialto 600 is the cheaper watt - about $9 per watt against $12. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam A15 B AudioControl Rialto 600
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?
AudioControl Rialto 600 is the easier recommendation: it leads on most of the measured areas and costs less. Take Arcam A15 if one of the "depends" rows above describes your system. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - AudioControl Rialto 600 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you play records, Arcam A15 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.