  The fusion excitation functions have been measured with rather good accuracy
for 32S+90Zr and 32S+96Zr near and below the Coulomb barrier. The sub-barrier
cross sections for 32S+96Zr are much larger compared with 32S+90Zr.
Semi-classical coupled-channels calculations including two-phonon excitations
are capable to describe sub-barrier enhancement only for 32S+90Zr. The
remaining disagreement for 32S+96Zr comes from the positive Q-value
intermediate neutron transfers in this system. The comparison with 40Ca+96Zr
suggests that couplings to the positive Q-value neutron transfer channels may
play a role in the sub-barrier fusion enhancement. A rather simple model
calculation taking neutron transfers into account is proposed to overcome the
discrepancies of 32S+96Zr.
