No single best speaker here - they are built to different priorities, and the right one depends on your room, your sources and what you listen to.
| Area | Better | Why |
|---|
| Bass | A | Triangle Borea BR03 BT digs deeper - 56Hz against 68Hz. |
| Built-in power | evenly matched | Similar onboard amplification (100W vs 120W RMS). |
| Connections | evenly matched | The same set of inputs and streaming options. |
| Size | depends | Klipsch R-51PM is easier to place; Triangle Borea BR03 BT is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Triangle Borea BR03 BT: a sub output; Klipsch R-51PM: a sub output. Klipsch R-51PM sits in a wider range (5 models), so a matched surround system is easier later. |
| Price | evenly matched | Much the same money ($599 vs $599 a pair). |
A Triangle Borea BR03 BT 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?
Triangle Borea BR03 BT has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 68Hz anyway, so judge these on the other rows instead. In a large or open-plan room, Triangle Borea BR03 BT 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.