  We apply the holographic principle to a flat dark energy dominated
Friedmann-Robertson-Walker spacetime filled with a tachyon scalar field with
constant equation of state $w=p/\rho$, both for $w>-1$ and $w<-1$. By using a
geometrical covariant procedure, which allows the construction of holographic
hypersurfaces, we have obtained for each case the position of the preferred
screen and have then compared these with those obtained by using the
holographic dark energy model with the future event horizon as the infrared
cutoff. In the phantom scenario, one of the two obtained holographic screens is
placed on the big rip hypersurface, both for the covariant holographic
formalism and the holographic phantom model. It is also analyzed whether the
existence of these preferred screens allows a mathematically consistent
formulation of fundamental theories based on the existence of a S matrix at
infinite distances.
