Watts are a proxy for current. So, they may not correctly reflect their performance.
Additionally, there is the old adage that tube watts are more powerful than equivalent than solid state watts… We should avoid discussing this… too many variables and theories to be valuable, and old tales.
91db is pretty good sensitivity. Does this does not put into the need massive power class to drive. But will likely start endless discussions of the impedance of the speakers.
There are a number of tube integrated amps of 50watts or greater that will power these well provided you are not into head banging levels of volume. Used I would think you could snag something really good.