This question seems to keep coming up. There is no experimental data on the reaction of N-benzylphenethylamines with MAOs. However, if you compare the relative reactivity of phenethylamines and benzylamines, the phenethylamines are about 25-fold more reactive. This suggests that the reaction of N-benzylphenethylamines with MAO will occur preferentially on the phenethylamine side, giving phenylacetaldehydes and benzylamines, not phenethylamines and benzaldehydes. In support of this hypothesis, I have also docked 25B-NBOMe into the structure of MAO-A (after removing the bound harmaline), and the preferred pose is the one where the phenethylamine substructure is spatially closer to the flavin cofactor.