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 | A | NAD Masters Series M33 has more power - 200W against 150W into 8 ohms. That is about 1.2dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (380W and 300W). |
| Noise floor | A | NAD Masters Series M33 is the quieter design on paper - 120dB against 100dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board. Primare I35 Prisma goes higher - 768kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | evenly matched | Only NAD Masters Series M33 has BluOS; only Primare I35 Prisma has Chromecast. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | B | Primare I35 Prisma takes more analogue sources - 5 against 2. |
| Phono stage | depends | NAD Masters Series M33 has a built-in phono stage (MM,MC) and Primare I35 Prisma 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 | evenly matched | The same expansion options on both. |
| Headphones | depends | Only NAD Masters Series M33 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | B | Primare I35 Prisma costs less - $5,795 against $6,499 at list. |
A NAD Masters Series M33 B Primare I35 Prisma
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 you play records, NAD Masters Series M33 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.