Here is the statement made by Jena Labs regarding Dry Ice:
Several audio writers, equipment modifiers, and so-called technologists have promoted refrigeration of cables and electronic parts by packing in Dry Ice. This is NOT cryogenic treatment. It results in only minor and temporary improvement. Even gas bath refrigeration in a cold furnace cooled by LN2 will not provide a sufficient chill. Scientifically speaking, Cryogenics refer ONLY to temperatures at or below the vapor point on Nitrogen, -320.4° Fahrenheit. Our process involves temperatures that are substantially colder than this. Clearly, dry ice has nothing to do with Cryogenics. Only true Liquid Nitrogen Immersion, as employed by JENA LABS will fully and permanently enhance the musical behavior of metallic conductors.