These are not the same size of amplifier: NAD C 368 BluOS-2i has roughly 2x the power of NAD C 328. That is about 3dB, 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 | NAD C 368 BluOS-2i has more power - 80W against 40W into 8 ohms. That is about 3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate NAD C 368 BluOS-2i the better fit for a mid-size room, a large room and a very large room, and NAD C 328 for desk or near-field listening and a small room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output barely increases (80W and 40W). |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (98dB vs 100dB). |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | A | Only NAD C 368 BluOS-2i has AirPlay 2, Roon and BluOS. |
| Analogue inputs | evenly matched | The same number of line-level inputs (2). |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | NAD C 328 takes up about 27% less shelf area (1349cm² against 1840cm²), and it is 113mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | NAD C 328 costs less - $699 against $1,749 at list. |
| Watts per dollar | B | NAD C 328 is the cheaper watt - about $17 per watt against $22. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A NAD C 368 BluOS-2i B NAD C 328
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?
NAD C 368 BluOS-2i is ahead, but on only 1 of the measured areas, and it costs about 2.5x the price. That is a lot of money for a narrow margin - NAD C 328 is the sensible buy unless a specific feature above decides it for you. 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 - NAD C 368 BluOS-2i has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 40 watts is already more than most people ever use, and the extra 40 watts would be headroom you pay for and never hear - we rate NAD C 368 BluOS-2i poorly for near-field use for exactly that reason. Think about the whole system: the roughly $1,050 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.