I did massive,massive doses for around one and a half years, of extremely pure mdma. I have some receptor problems, but relative to what I gained, I gladly accept the trade-off.
There are multiple levels the whole 'x' experience can be taken to.
The empathogen effects are low dose responses, ala shulgin. Not to say they aren't there with higher doses, but the other stuff overwhelms the more subtle shades. As already mentioned, the conversion of mdma ro mda in the liver via demethylation make for a hallucinogenic experience if you're taking a lot.
We did it about once a week for around two days per session. I'm talking start fri night and stop sunday afternoon. One long session.
Thats about thirty hours or so, continual. I don't know other people who did it this way. You only experience mdma for the first few hours, then it's all mda-type. Hallucination city.
Since I was making it at the time, I had enough to take as much as I liked. 300 doses was costing me about 20 bucks....
You would reach a titration zone with it, where you could take a pill
every few hours, and stay in that space a long, long time....obviously, once the blood serum level reaches a certain point, taking a pill periodically is outrunning your bodies ability to metabolize it.
There are FAR more experiences in that area than what I've read on the net.
But there has to be HIGH doses, and everyone has a different capacity for these things so I cant sat I'd advise everyone to do that.