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 | Harbeth SHL5plus XD2 digs deeper - 40Hz against 54Hz. |
| What you buy | depends | ATC SCM19A is a complete system - just add a source. Harbeth SHL5plus XD2 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | With Harbeth SHL5plus XD2 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | Harbeth SHL5plus XD2 can be re-amped later and outlive several amplifiers; ATC SCM19A ages as one unit. |
| Size | depends | Harbeth SHL5plus XD2 is easier to place; ATC SCM19A is bigger, which usually goes with fuller bass. Your room decides. |
| Type | depends | A Powered Floor-standing against a Passive Bookshelf - a different job rather than a better one. |
| Cabinet | depends | Sealed vs Ported. Sealed is tighter and happier near a wall; ported digs lower but wants space behind it. |
| Price | B | Harbeth SHL5plus XD2 is cheaper - $7,990 against $8,999, about 11% less. Speakers only - an amplifier narrows that gap. |
A ATC SCM19A B Harbeth SHL5plus XD2
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 SCM19A suits you if you want one box, ready to play, with nothing else to buy. Harbeth SHL5plus XD2 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 54Hz anyway, so judge these on the other rows instead. Match it to your room: we rate ATC SCM19A the better fit for near-field listening and a small room, and Harbeth SHL5plus XD2 for a mid-size room and a large room.
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.