  We complement our earlier position-space exploration of a recently proposed
S-matrix for transplanckian scattering by a momentum-space analysis. As in the
previous paper, we restrict ourselves to the case of axisymmetric collisions of
extended sources. Comparison between the two formulations allows for several
cross-checks while showing their complementary advantages. In particular, the
momentum-space formulation leads to an easier computation of the
emitted-graviton spectra and to an attempt to study the system beyond its
critical points into the presumed gravitational-collapse regime.
