How to Separate and Insulate AC and IC cables

My set up forces me to run my interconnects and my power cords and my speaker cables through a 3" hole behind my amplifier. I know this is audio sin, but I need to keep my components where they are; it's a custom built maple and slate wall cabinet/shelving system. I've thought about drilling two other holes down through the shelf behind my amp, which would separate the cables at that point, but I'm shy about drilling into my new cabinetry.

Here's what I'm considering:

I want to insulate my cables and cords from each other using some sort flexible tubing. I've contemplated garden hose, clear plastic hose, pipe insulation. Is this adviseable? What are the drawbacks of doing this? Anyone know of a cost friendly product that would serve my purpose?