Different price classes - Onkyo TX-RZ70 costs roughly 2.1x what Onkyo TX-RZ30 does. Expect it to lead on paper; the question is whether you will hear the difference through the speakers you own.
| Area | Better | Why |
|---|
| Power | B | Onkyo TX-RZ70 has more power - 140W against 100W into 8 ohms. That is about 1.5dB, which is a small step in loudness but real headroom on peaks. |
| Analogue inputs | A | Onkyo TX-RZ30 takes more analogue sources - 6 against 4. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Onkyo TX-RZ30 takes up about 20% less shelf area (1753cm² against 2205cm²), and it is 103mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Onkyo TX-RZ30 costs less - $1,100 against $2,300 at list. |
| Watts per dollar | A | Onkyo TX-RZ30 is the cheaper watt - about $11 per watt against $16. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Onkyo TX-RZ30 B Onkyo TX-RZ70
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?
Onkyo TX-RZ30 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. Think about the whole system: the roughly $1,200 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.