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 | A | Fluance Ai81 digs deeper - 30Hz against 45Hz. |
| What you buy | depends | Fluance Ai81 is a complete system - just add a source. Sony SS-CS3 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | Fluance Ai81 has Bluetooth built in. With Sony SS-CS3 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | Sony SS-CS3 can be re-amped later and outlive several amplifiers; Fluance Ai81 ages as one unit. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | A | Fluance Ai81: a sub output. |
| Price | evenly matched | Much the same money ($499 vs $458 a pair) - though the passive pair still needs an amplifier. |
A Fluance Ai81 B Sony SS-CS3
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?
Fluance Ai81 suits you if you want one box, ready to play, with nothing else to buy. Sony SS-CS3 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 45Hz anyway, so judge these on the other rows instead.
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.