The 99 THX DVD has issues in regards to the mono sound, primarily it being overly compressed DD. The Criterion laserdisc PCM blows it to pieces. It's like the 192k DD mono audio for The Terminator on DVD. It pales compared to the PCM audio on the laserdisc. Night and day.
I actually hate all the remixes for HALLOWEEN. They added some kind of weird reverb to the music so it sounds wonky.