A generation apart: Kanto TUK G2 is the newer design, against a 2018 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 | Kanto TUK G2 digs deeper - 50Hz against 68Hz. |
| Built-in power | evenly matched | Similar onboard amplification (130W vs 120W RMS). |
| Connections | B | Klipsch R-51PM adds phono. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | depends | Kanto TUK G2: a sub output; Klipsch R-51PM: a sub output. |
| Price | B | Klipsch R-51PM is cheaper - $599 against $900, about 33% less. |
A Kanto TUK G2 B Klipsch R-51PM
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and your own room settle it. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 68Hz anyway, which makes the cheaper Klipsch R-51PM much easier to justify. Think about the whole system, not just the speakers: the roughly $301 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.