Jeffcott. I have found that if you use stock PCs then when you put a dedicated line in, that you will hear an improvement in dynamics and soundstage size, but you will find the sound can be brighter and with a coarser grain. Systems that sounded acceptable with stock PCs, became more fatiguing to listen to with a dedicated feed. When decent PCs are used for every component, then the overall improvement over a non-dedicated feed can be stunning. I have experienced this with around a dozen instalations.
The Romex you have in the US may be different from what we use in NZ (and we call it TPC). But of the three types I have tried, each was quite directional. When used in the wrong direction the sound was relatively thin and flat with a fat indistinct bass. When used in the right direction the sound was more vivid and natural, with better depth, better bass articulation and rhythm. What I have done each time is run the cable from the switch board to the components through the house (ie. not in the wall yet), in one direction and then the other. The difference in sound has been quite marked with each of the three makes of cable available here.
I won't comment on grounding. For a start the topic is big, and has been covered elsewhere in Audiogon. More importantly, when reading through what Americans found was best to do I discovered how different the 115V supply there is to the 230V supply here - with critical differences about ground arrangements.