Well, methadone is exerting effects on serotonin system, so I would imagine that there would be more interactions between methadone and mdma than buprenorphine and mdma.
Regarding experience being different when combining buprenorphine and mdma, it surely is different than if only mdma is taken. Another important thing is the difference between person being on a stable buprenorphine dose vs person being high on buprenorphine, while taking mdma. Every opioid will take away from mdma experience the clarity, intense, empathic side...as opioids are sedatives/narcotics in nature and are also competing for dopamine. But the question was will buprenorphine "block" mdma and, although it will make the experience duller and different it will not block it entirely. If one has tolerance for buprenorphine than taking mdma will give him different but still pleasant experience. Again, it will not be the same as it would be without one being on buprenorphine but ther will be great reduction of anxiety, depression will be lifted, feeling of warmth in the body, feeling that all is good... In the end it is all individual, but that was it like for me.
Take care!