Well good I do see two peaks! But if not the resonance of my drivers, what is the peak at 30Hz?

The low pass of the bandpass.

You are tuned at 30Hz & 75Hz.

Bandpass will have two filter components, a low pass & a high pass.

ok, ok so commented before, which is better?

increase or lower, the impedance rise for a better spl in some frequency, ejem-50hz . and because?

For a strictly spl oriented setup logic says it's better to have an impedance as low as possible (at the peak frequency), to extract the most out of the amplifier you are using.

For a setup which plays music I wouldn't bother too much with the impedance curve.