Minimum recommended amplification requirements and amplifier matching

I agree with Willem and hifiman. There's more to driving speakers than the 90dB spec, and we don't know if the stated sensitivity is rated for 8 ohms or 4 ohms.
In addition to sensitivity, the impedance curve is an important factor; how much power will be required to satisfactorily drive the load throughout the frequency range; eg, does the amp have the power to drive the bass frequencies or react to peaks and transients without clipping.

If it’s a "recommendation" and a "requirement" at the same time, I’d consider this "unusual". Typically this should be something like "recommend amplifier power", etc.

It most likely will sound "loud enough", but, with respect to the referenced speaker and amp, 3 important questions:
1.  Was it designed/voiced for a solid state or tube amp and particularly what does the impedance curve look like at the frequency extremes. 
2.  What is the dynamic range of the music you listen to?  Power requirements rise exponentially on peaks. 
3.  Do you plan to run it in triode or ultra-linear mode? 

I would recommend a preamp with a gain of over 20 with a tube amp. My CAT preamp with a gain of 26 drives my 3 watt 2A3 amp to realistic levels connected to a pair of 86 db Thiel 3.6's. Of course that applies to things like solo instrument and chamber music. When it comes time for a Mahler 8 or a Bruckner 9 the Levinson beasts get called up to the plate.

More importantly, can you audition those speakers with your amp?    Specs are great but don’t always tell the whole story.  I was driving a pair of 87dB eff speakers with a 40 watt el34 amp and it was plenty loud for me in a 17 x 15 x 9 room.   Current speakers are 99 dB eff and it’s ridiculous with just 40 Watts.