How are you defining dynamics? This sounds like that AVS thread.
I can't speak for the ACI speakers. I'm sure they are great, they are also twice the price.
Anyway, I had a friend over a while back when I was demoing speakers. He brought his SPL meter which can hold values for the min and max levels. Then we played the same Mahler passage on each speaker, subtracted the min spl from the max spl, and there you get dynamics. IIRC, we were testing in room with volume ranging ~55db and 90db.
Ascend 340SE: 32db
Paradigm Studio 40: 33db
DIY MTM (judged the best of the bunch): 31db
Those measurements weren't supper accurate, the meter was being held by hand. I would say that the dynamic range was close enough in all of them that they could be considered the same. I think when people start talking about dynamic range differances with speakers of such similar size and design, they are full of crap. They might be hearing differances, but I don't think dynamic range is the correct descriptor. I think that people who talk about dynamice range are really refering to is max output capabilities before breakup occures.
My room is about 3000cu ft, and has an open stairway to the upstairs. I listen to movies at ~-10. I think my receiver and room is holding me back from approaching referance more than the speakers.
In my opinon, if you have the cash for the ACI speakers, get them. I'm sure you will be very happy. If you would like to spend a little bit less, get the Ascends. Again, I think you will be happy with them. If not, they arn't that expensive to ship back.