Different kinds of product: one is active with its amplifier built in, the other passive and needs one. Judge them on how you want to own the system, not just the specs.
| Area | Better | Why |
|---|
| Bass | A | Q Acoustics M40 digs deeper - 38Hz against 79Hz. |
| What you buy | depends | Q Acoustics M40 is a complete system - just add a source. KEF LS50C Meta also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | Q Acoustics M40 has Bluetooth and streaming built in. With KEF LS50C Meta that all comes from the amplifier you pair it with. |
| Upgrade path | depends | KEF LS50C Meta can be re-amped later and outlive several amplifiers; Q Acoustics M40 ages as one unit. |
| Size | depends | KEF LS50C Meta is easier to place; Q Acoustics M40 is bigger, which usually goes with fuller bass. Your room decides. |
| Type | depends | A Powered Floor-standing against a Passive Center Channel - a different job rather than a better one. |
| Expandability | A | Q Acoustics M40: a sub output. |
| Price | evenly matched | Much the same money ($999 vs $900 a pair) - though the passive pair still needs an amplifier. |
A Q Acoustics M40 B KEF LS50C Meta
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 speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Q Acoustics M40 suits you if you want one box, ready to play, with nothing else to buy. KEF LS50C Meta suits you if you already have an amplifier, want to choose the electronics, or expect to upgrade in stages. Neither is the better speaker in the abstract. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 79Hz anyway, so judge these on the other rows instead. In a large or open-plan room, Q Acoustics M40 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, KEF LS50C Meta is the easier speaker to get right.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.