The thing that makes modern arrangers sound so great isn't really a stacking thing. SA/DNC sounds are so good because of sample switching, not stacking and layering, generally. In other words, you get different voices (or oscillators, or samples, whatever you want to call them) sounding depending on how you play. Play staccato, get one sound. Play legato INSTEAD of the staccato, you get the legato sample. But only ONE voice is being used...

Drum sounds, same thing. Many modern arranger's drum sounds have four or so different samples, for gradually increasing velocities. But only one plays at a time. Some of the big drum VSTi's have as many as 64 samples per drum (or more), but you are only hearing the one per note.

I agree with Dennis and Nigel... there are FAR more important things to worry about than maxing out a 128 voice arranger!