you can also try using midi cc # 73 which will adjust the overall attack length.
from p.50 of the manual:
The following controllers are hard-wired:
CC7 = Volume
CC11 = Expression
CC64 = Sustain (can be enabled/disabled perelement
using display control)
CC66 = Sostenuto (can be enabled/disabled perelement
using display control)
CC73 = Global Amplitude Attack
CC72 = Global Amplitude Release