These sit in different price classes - Sony Signature Series SA-Z1 costs roughly 6.2x what KEF LSX II does. Expect it to lead on paper; the question is whether the gap is audible enough in your room to be worth it.
| Area | Better | Why |
|---|
| Bass | B | Sony Signature Series SA-Z1 digs deeper - 51Hz against 54Hz. A subwoofer would even that out. |
| Built-in power | evenly matched | Similar onboard amplification (200W vs 212W RMS). |
| Connections | A | KEF LSX II adds Bluetooth, Wi-Fi, streaming and HDMI. |
| Size | depends | KEF LSX II is easier to place; Sony Signature Series SA-Z1 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | A | KEF LSX II: a sub output. |
| Price | A | KEF LSX II is cheaper - $1,299 against $8,000, about 84% less; arguably a different class. |
A KEF LSX II B Sony Signature Series SA-Z1
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?
KEF LSX II has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. In a large or open-plan room, Sony Signature Series SA-Z1 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. Think about the whole system, not just the speakers: the roughly $6,701 saved by taking the cheaper pair would buy a subwoofer or a better amplifier, and either usually does more for the sound than the difference between these two.
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.