Assuming the S8e (which I owned for a few years) has an impedance curve similar to the S5e (quite likely), using a tube amp will be less than optimal.Interestingly, I would say otherwise. Tube amps maintain a greater constant power output over a wider impedance range. This is why they are more often mated with Electrostatic speakers like Sound Labs which have a high impedance down in the lower frequency range.
From the experience as reported by Grimace, tube amps seem to work quite well here.