Linkwitz showed an example of how he used the nomographs (you can do the same with the formulas he provided too) to size the drivers of a speaker system. I'd suggest that you read through it first.
He didn't show how to calculate (from fundamental physics) how much voltage (power is a mostly irrelevant metric) to drive the drivers to produce his SPL targets. However, you can easily do that by reading the sensitivity spec or frequency response graph off the speaker driver datasheets. Remember Linkwitz's calculations are for radiating to full space. Speaker drivers are measured when mounted to an infinite baffle, so they are radiating to half space and for LF, that means 6 dB higher SPL than Linkwitz's numbers.
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The electrical power efficiency (i.e. the SPL-to-power relationship at a given frequency) can be obtained by calculating the current required using the impedance plot, and multiplying it with the signal voltage. That will give you the apparent power (in VA). If you also have the phase plot, you can multiply the apparent power and the cosine of the phase angle to get the real power. But please note that this does not take into the account of any cross-over filters (and as the Linkwitz speaker designs are active multi-ways, the speaker drivers are directly connected to the amplifiers).
If you are interested in the electrical power required from basic physics, I can start a new thread to show the mathematics on how this can be done from the Thiele-Small parameters.
