while both MDMA and its beta-ketone analog (methylone) promote the release of dopamine to some extent, only methylone appreciably inhibits its reuptake. So combining methylone and methoxetamine causes this to occur in your brain:
1) Moderate release of serotonin
2) Moderate inhibition of serotonin reuptake
3) Moderate release of norepinephrine
4) Moderate inhibition of norepinephrine reuptake
5) Moderate release of dopamine
6) Moderate inhibition of dopamine reuptake
4) Strong inhibition of dopamine reuptake
5) Strong antagonism at NMDA receptors
6) Possible weak agonism at Mu-Opioid receptors *(see above)*
MDMA possesses some agonistic activity at serotonin receptors. Relevantly, MDMA is a weak 5-HT2a agonist, which should negate some of the toxicity induced by methoxetamine's antagonistic effects at NMDA glutamate receptors. This fact, in addition to the drug's minimal effect on the reuptake of dopamine (in the sense that it is not compounding methoxetamine's inhibition of dopamine reuptake in the same manner that an equipotent dose of methylone would be expected to induce), may contribute to MDMA's subjectively better synergy with methoxetamine than that of its beta-ketone analog.
AMT is actually a strong triple-releaser, and a moderate triple-reuptake-inhibitor, and it possesses more notable pharmacological mechanisms than I have the time or energy left to go into in detail. Notably, it's a moderate non-selective serotonin agonist, and if I remember correctly, it even possesses D1 dopamine agonistic properties. I've heard nothing but good things about its combination with MXE, though, so who knows what's going on there? Actually, I know the answer to that question. Nobody. Nobody knows the details of what exactly happens when you combine AMT and MXE.