memory allocation for vision dsp Options

I'm hopping that someone can help me with this on going problem I've been having running
Vision on an iMac 350mhz.

The problem being that it's always stopping (not freezing) in mid operation ,(midi only. No
audio) and the cpu performance window pops up. I've tried setting and re-setting the
minimum and preferred sizes in the memory allocation window within the suggested ranges
all to no avail. I've got 128 megs of ram which should be more than enough,as well as all
extraneous extensions turned off.

Any suggestions to resolve this problem as well as simply improve overall performance
would be greatly appreciated.

Thanks in advance,

Gep