Here's an unreleased Leviathan song from 2002 or so that includes a memorable Lurker of Chalice section (Minions, sped up). It features similar guitar sweeps to the ones that Deathspell Omega was using years later.
The Tenth Sublevel of Suicide demo is almost entirely different than the proper release. I think one song appears on both. It has more in common with Lurker of Chalice and the Tentacles of Whorror album. The unreleased parts are pretty high quality. Non-fans aren't going to swayed, but anyone who enjoys early Leviathan will be into this.