Actually, in the back of the rack there's very little heatshrink showing. I use 4-, 8-, and 16-conductor jacketed multipair cable from ProCo and Gepco for the runs from the rack- so what you see in there is just the stripped-back multipair cable. Essentially, what I built is multiple snakes terminated on the bays: so all 16 direct outs are on one multipair, all 16 line ins on another, all 16 inserts are on another, the stereo ins and outs for a reverb are on 4-pair, and so on. Makes it easier to keep straight at the board end, where everything fans out to 1/4" TRS connectors.
Why shrink, when you can get multipair and just strip back the jacket? (;-)
I use tons of heatshrink elsewhere, but very little back there.