These sit in different price classes - Klipsch The Sevens II costs roughly 3.3x what Klipsch R-51PM 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 | A | Klipsch The Sevens II digs deeper - 39Hz against 68Hz. |
| Connections | A | Klipsch The Sevens II adds HDMI. |
| Size | depends | Klipsch R-51PM is easier to place; Klipsch The Sevens II is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Klipsch The Sevens II: a sub output; Klipsch R-51PM: a sub output. |
| Price | B | Klipsch R-51PM is cheaper - $599 against $1,999, about 70% less; arguably a different class. |
A Klipsch The Sevens II 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?
The usual trade-off: Klipsch The Sevens II measures better, Klipsch R-51PM costs about about 3.3x the price% less. Whether that gap is worth the money is the call only you can make - and in a normal room it is often smaller than the numbers suggest. 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. In a large or open-plan room, Klipsch The Sevens II has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Klipsch R-51PM is the easier speaker to get right.
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.