........to complete my project (speaker and passive pre).
Did you mean passive
crossover or did you build a passive preamp?
1. If you're going to use a passive pre-amp with inefficient speakers, the amplifier that you choose
must have plenty of
gain, not necessarily a lot of power. 26 to 30 dB of gain is a good place to start for such a situation. If you can't find the gain spec for your amplifier, the other way to figure out how much gain it has is to check the sensitivity spec. Something in the 150mV to 500mV range would be good, and anything above that, such as the 1V to 2V range, will probably require an active pre amp.
This is one reason why so many lower powered tube amps work fine with passive pre amps and inefficient speakers. They usually have a lot of gain.
2. If you buy an integrated amplifier, you won't need a passive pre. Which means :
3. I have a feeling you meant passive
crossover and speaker, so never mind all of that . . . .
(It's still worth mentioning though, because understanding the system gain structure helps us to evaluate the sound of things as we put different components together.)