What commented out section do you refer to?
Ack voices are automatically freed on end of the AR volume envelope or cut when a new trigger is received for a running voice (voices are monophonic, basically). Gate could in some way be exposed to release voices before AR envelope is released, ie. with a new ”release” command.
I don’t consider Ack a general purpose sample player, though. Ideally, such an engine would feature a ADSR envelope for volume and gate on/off. Should be noted also that SuperCollider has a couple of UGens specific to single-cycle waveforms that might lead to better results.
Have you tried loading single-cycle waveforms in Ack?