These sit in different price classes - Kanto TUK costs roughly 1.7x what Kanto YU6 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 | evenly matched | Much the same reach (50Hz vs 50Hz). |
| Built-in power | B | Kanto TUK has the bigger amplifier (130W vs 100W RMS). |
| Connections | evenly matched | The same set of inputs and streaming options. |
| Size | depends | Kanto YU6 is easier to place; Kanto TUK is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Kanto YU6: a sub output; Kanto TUK: a sub output. |
| Price | A | Kanto YU6 is cheaper - $540 against $900, about 40% less; arguably a different class. |
A Kanto YU6 B Kanto TUK
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?
Kanto TUK is ahead, but only on 1 of the measured areas, and it costs about 67% more. That is a lot of money for a narrow margin on paper - Kanto YU6 looks like the sensible buy unless something else about the Kanto TUK appeals to you. In a large or open-plan room, Kanto TUK has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Kanto YU6 is the easier speaker to get right. Think about the whole system, not just the speakers: the roughly $360 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.