I guess the manual for the 4000 wasn't as thorough.
I've ran into a few like that.
I've only used "latch" for the trigger mode and that only worked with the numpad on ESI 32. So based on that I think that 'latch' only applies to the numpad and not to keyboard. Although if ESI 4000 has extra trigger options for its zones there could be some hope.
But if for some reason you can't have the "latch" function enabled for MIDI zones then what you could try is setting up an infinite Amp envelope release time for the zone that you want to sustain (or simply setup a "one shot) playback mode that plays the sample through its entirety regardless of envelope settings) and basically group that zone with another zone. That way if the sample is playing through and you want to stop it all you do is hit a keyzone grouped to it and the sound will cut off. I usually setup "silent" zones just for that. Think of it as an open/closed hihat effect where the "silent" zone acts as a closed hihat. Not sure if I'm making sense.
-ED-
[This message has been edited by 3351 (edited 02-07-2007).]