A generation apart: KLH Concord is the newer design, against a 2017 model. Newer is not automatically better, but the older one is more likely to be discounted or near run-out.
| Area | Better | Why |
|---|
| Bass | A | KLH Concord digs deeper - 28Hz against 58Hz. |
| Amplifier needs | A | KLH Concord is more sensitive (94dB vs 87dB), so it goes louder on the same amplifier. |
| Headroom | A | KLH Concord takes more power (225W vs 130W) - more in hand in a big room. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Cabinet | depends | Ported vs Passive Radiator. |
| Expandability | B | KEF Q550: Atmos drivers. |
| Price | A | KLH Concord is cheaper - $1,000 against $1,400, about 29% less. |
A KLH Concord B KEF Q550
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?
KLH Concord is the easier recommendation: it leads on most of the measured areas and costs less. Take KEF Q550 if its size, looks or fit in your room suit you better. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 58Hz anyway, so judge these on the other rows instead. If your amplifier is modest, vintage or valve-based, KLH Concord is the safer partner - the other will want more current or more watts to sound its best.
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.