A floor-standing against a bookshelf. They are built for different places in a room, so start with where these have to go rather than which looks better on paper.
| Area | Better | Why |
|---|
| Bass | A | Q Acoustics M40 digs deeper - 38Hz against 54Hz. |
| Built-in power | B | KEF LSX II has the bigger amplifier (200W vs 50W RMS). |
| Connections | B | KEF LSX II adds Wi-Fi and HDMI. |
| Size | depends | KEF LSX II 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 Powered Bookshelf - a different job rather than a better one. |
| Expandability | depends | Q Acoustics M40: a sub output; KEF LSX II: a sub output. |
| Price | A | Q Acoustics M40 is cheaper - $999 against $1,299, about 23% less. |
A Q Acoustics M40 B KEF LSX II
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?
The usual trade-off: KEF LSX II measures better, Q Acoustics M40 costs about about 30% more% less. Whether that gap is worth the money is the call only you can make - and in a normal room it is often smaller than the numbers suggest. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 54Hz 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 LSX II 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.