Something like that can only be true if all other factors are equal. Things like impedance curve, type of xover used, driver size, ported or non ported bass, room placement, etc will all work the amp differently even though the sensitivity specs are the same.Zd, there is no need to split hairs. I don't disagree that these can cause minor differences, but since the power/sensitivity is a logarithmic relationship, they will not be significant to the basic calculations. Yes, room placement can increase certain frequencies, but that is a tonal balance issue, not an overall volume issue.
A good example of what I'm talking about is Wilson speakers. Even though they have fairly high sensitivity ratings, they're usually paired with big SS amps to control the bass. You can find many other speakers with the same xdb rating that are an easier load on the amp. And its those differences that will have an effect on volume without altering sensitivity.Sure there can be perceived differences when using different speakers on the same amp, but that doesn't change the basic science that I have previously stated. Here is an article that confirms my statement that you seem to doubt, and I hope it helps you to understand,
LetÂ’s talk about dBs, loudness, and sensitivity
Also, here is one of many online calculators that you can plug in the numbers and see that my calculations are correct, within a very slight margin of error.
AllegroSound
So again, the only choice the OP has to get an increase in volume is to use a speaker with higher sensitivity since he can't add more power to the current speaker. If you have another solution, I would really like to hear it.