I have combined MDMA, MDA and 2c-b 3 times. Everytime was amazing. I have done the MDMA/2c-b combo many many times, and the difference is that you basically roll harder with MDA, hallucinate more, MUCH more intense music. The only downside of the combo of three is that at some times it can be very intense, bordering sensory overload. But if you can handle that it is awesome. The combo gave me the strongest roll of my life (not in a magical/empathic sense, but mad rushing extreme visual and maximum music intensity). 2 times I dropped the MDA with MDMA, redosing with MDMA later, and finally redosing with 2c-b. Last time I took a full dose of MDA, redosed MDMA 2 times and finally dosed 2c-b. The 2c-b is always added around the 3-4 hour mark.
2c-b/MDMA combo is definately more safe and comfortable, and very magical. But the combo of three is for the brave, but if you dare it can blast you to space at a rave. Extremely intense. Take a slightly lower dose of 2c-b when combining with MDMA/MDA than with MDMA only as MDA is a psychedelic and they will greatly potentiate each other.
The strongest roll of my life, if I recall right, was an initial dose of 100mg MDMA and 75mg MDA, followed by 50mg MDMA redoses on the 1 and 2 hour mark and finally a 80mg MDMA and 18mg 2c-b dose at T3:00. When that final dose kicked in I rolled unbelievably hard. It was the only time I actually felt that I consumed an absolutely new drug, it was unbelievable, out of this world. Every bass felt like an earthquake and I was in a tent with 2000 people, and at that time I thought I was in a volcano. THAT intense.
Watch your body temperature on this combo!! You can get quite hot.