These are not the same size of amplifier: Rotel RB-1590 has roughly 2.8x the power of MOON 330A. 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 | A | Rotel RB-1590 has more power - 350W against 125W into 8 ohms. That is about 4.5dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Analogue inputs | evenly matched | The same number of line-level inputs (2). |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | A | Rotel RB-1590 is the cheaper watt - about $13 per watt against $35. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rotel RB-1590 B MOON 330A
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?
Rotel RB-1590 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. 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 - Rotel RB-1590 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 125 watts is already more than most people ever use, and the extra 225 watts would be headroom you pay for and never hear.
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.