You can't go on specs alone.
For one, they're often exaggerated.
Two, even if they were entirely honest, they may be measured with different equipment, different measurement techniques, etc, which will lead to different results.
And, three, the limited information given in such specs is not nearly enough to tell you about how a speaker sounds. It's like giving the length, width, height, weight and engine horsepower of a car and thinking that's enough to know exactly what the car will look like and how it will ride.
As for comparing with the BX-2, the BX-2 is a decent budget speaker, but the Sierra 1 or 2 will trounce it in every way. The Sierra 1 trounces the Monitor Audio Silver RX-1, so the Sierra 2 certainly trounces the lower-model BX-2.
Semi-retired Technology Insider.
Insist on Quality Posting.