  We show that only by performing generalized dimensional reductions all
possible brane configurations are taken into account and one gets the complete
lower-dimensional theory. We apply this idea to the reduction of type IIB
supergravity in an SL(2,R)-covariant way and establish T duality for the type
II superstring effective action in the context of generalized dimensional
reduction giving the corresponding generalized Buscher's T duality rules. The
full (generalized) dimensional reduction involves all the S duals of
D-7-branes: Q-7-branes and a sort of composite 7-branes. The three species
constitute an SL(2,Z) triplet. Their presence induces the appearance of the
triplet of masses of the 9-dimensional theory. The T duals, including a
``KK-8A-brane'', which must have a compact transverse dimension have to be
considered in the type IIA side. Compactification of 11-dimensional
KK-9M-branes (a.k.a. M-9-branes) on the compact transverse dimension give
D-8-branes while compactification on a worldvolume dimension gives
KK-8A-branes. The presence of these KK-monopole-type objects breaks translation
invariance and two of them given rise to an SL(2,R)-covariant ``massive
11-dimensional supergravity'' whose reduction gives the massive 9-dimensional
type II theories.
