My experiences parallel Rsbeck's regarding both amplifiers and digital. I'd start with dedicated lines and plug the amps into the wall. Regarding digital, I own a Sound Application plc and have dedicated lines. The Sound Application is a fine plc but it does not isolate components (nor does the Shunyata or Audio Magic). This means that if you plug preamp and digital components, or multiple digital components, into one plc, you do get a degree of digital noise cross-contamination. If you then isolate the digital via an isolation transformer plugged into the plc, you have a lot of excess daisy chaining of cords and conditioners, which inherently tends to kill sound and reduce resolution. The better alternatives are either to have separate dedicated lines for each component, with filtering or isolation on each of the digital components, or else to have a single isolating and conditioning unit for the front end, providing that you can find one that is high enough in quality with low noise and no coloration.
If you really want to avoid 'dedicated crap', then go all out and use a high kva isolation transformer to feed your dedicated circuits or subpanel, and an upgraded grounding system.
