Both are Yamaha, from different ranges - the engineering approach is shared and the differences are mostly in power, connectivity and price.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 110W against 100W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Analogue inputs | evenly matched | The same number of line-level inputs (3). |
| Room to grow | A | Only Yamaha AVENTAGE RX-A4A offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Shelf space | depends | Yamaha AVENTAGE RX-A2A takes up about 14% less shelf area (1712cm² against 2003cm²), and it is 67mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Yamaha AVENTAGE RX-A2A costs less - $1,200 against $1,600 at list. |
A Yamaha AVENTAGE RX-A4A B Yamaha AVENTAGE RX-A2A
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?
Yamaha AVENTAGE RX-A4A is ahead, but on only 1 of the measured areas, and it costs about 33% more. That is a lot of money for a narrow margin - Yamaha AVENTAGE RX-A2A is the sensible buy unless a specific feature above decides it for you. Think about the whole system: the roughly $400 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.