Different price classes - Denon PMA-900HNE costs roughly 1.7x what MISSION 778X 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 | evenly matched | Effectively the same output - 45W against 50W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Denon PMA-900HNE holds up better into a 4-ohm load: its output increases strongly to 85W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Built-in DAC | A | Both decode on board. MISSION 778X goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Price | A | MISSION 778X costs less - $549 against $949 at list. |
| Watts per dollar | A | MISSION 778X is the cheaper watt - about $12 per watt against $19. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A MISSION 778X B Denon PMA-900HNE
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?
MISSION 778X has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Denon PMA-900HNE is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. 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.