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 | B | Klipsch La Scala AL5 digs deeper - 51Hz against 55Hz. A subwoofer would even that out. |
| What you buy | depends | ATC SCM20ASLT is a complete system - just add a source. Klipsch La Scala AL5 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | With Klipsch La Scala AL5 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | Klipsch La Scala AL5 can be re-amped later and outlive several amplifiers; ATC SCM20ASLT ages as one unit. |
| Size | depends | ATC SCM20ASLT is easier to place; Klipsch La Scala AL5 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | B | Klipsch La Scala AL5: bi-amping. |
| Price | evenly matched | Much the same money ($12,499 vs $12,998 a pair) - though the passive pair still needs an amplifier. |
A ATC SCM20ASLT B Klipsch La Scala AL5
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?
ATC SCM20ASLT suits you if you want one box, ready to play, with nothing else to buy. Klipsch La Scala AL5 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. In a large or open-plan room, Klipsch La Scala AL5 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, ATC SCM20ASLT 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.