I've always just cut some small slots in the back to route cabling through. It provides a path for air circulation and preserves the clean look of the rear panels to hide what's going on in the back.
I like Salamander racks for their depth and adjustable shelving.
I use two (2) Twin 30 units side by side with the backs in place, cut as mentioned above for the cabling to pass through to the back.
Excuse the mess...I was totally re-doing the system at the time I took the picture.
