Drawding, you say:
"Also keep your PC away from your interconnects or if they must cross have the cables at 90 deg to each other."
Here you locked onto one way well designed cables can help your "system" by helping to address the cluttered "cable ecosystem" often found behind our gear. I cannot tell you how a good PC does or does not "clean up" power from the wall to your equipment (garbage into cable - 4 star power dinner out? OK, maybe), but it only makes sense that reducing stray electrical fields and interference between high current cables and low current cables in the vaccinity of your amp and source can yield real gains in fidelity. Better cable geometry and shielding across all applications behind your gear helps solve the same problems as keeping "your PC away from your interconnects" in physical space.
Al, terrific input here as usual. I agree with your assessment of the unique applications presented by the LS50's. Two issues come to mind:
One, there is unlikely very much other wire clutter behind your speakers, so the benefit of a better shielded PC to reduce interference with IC's and speaker cables all exiting the same amp or reciever i describe above is essentially moot. This leaves a more solid connection to speaker and power outlet as a potential advantage of a better cable with better connectors, along with improved match of metallurgy, dielectric and wire geometry with the properties of what are really very complicated speakers with many things going on inside them as Al notes.
Two, given the complex devices, I might look at PCs that would work well with modestly powered but quality switching AVRs that contain both amplification and digital circuitry. You need to supply juice for 230wpc of switching power, right? Suggestions by others above to focus on smaller gauges common for digital applications versus heavy "garden hose" PCs seem warranted as taming digital artifacts may be more important than raw current for this application, and very heavy cables on small speakers may present physical stability issues. But YMMV.
In my experience, better cables across the board make a positive and sometimes radical difference in sound, but as suggested by others, you just have to try several solutions to see what works best in your application. I like the idea of contacting the Cable Co. and asking their advice for 2-3 cables to send you in your price range to try with the KEFs (and the Node?) and listen for yourself to see which cables sound better, if any, compared to the stock PCs.
Finally, you may want to try at least one power conditioner and move between the speakers and the Node 2 in order to see if that helps improve your sound. You may decide you need two if the Node and speakers are far apart and both show benefit.
Good luck,
kn