Can't change buffer size from Samplitude

[JLM1]

Hello all,
I use my DM4800 with Samplitude.
I changed from Samp 10 to ProX2 and simultaneously from XP to W7/32.
If I remember correctly, I could access the IFFW control panel from Samp (Options-> Audio system) and change the size of the buffer. Now I can access the control panel but I can't change anything. If I want ot change the buffer size, I need to exit Samp and access the control panel directly.
Thanks in advance for your help.
JLM