For my system, it is not a subtle improvement.
I get fuller over all sound with the Soundstring PC, which results in much more bass. Now I am seriously contemplating bass traps for my room. If I were to quantify the differences in "bass response" I give stock cables 4, Signal Cables 6, and Soundstring 8 (scale of 1 to 10).
My friend's opinion was that somehow I was not getting enough power to my Quads before, and that now I am experiencing the full potential of the Quads. I am not sure if PC's actually "color the sound" e.g. add more bass, or have characteristics.
I do believe that everyone's experience will be different, and it will vary depending on the system. Since I am still burning in my CT6 preamp, and the cardas golden cross IC between the preamp and MV60 amp, I plan to wait awhile before making any decisions on the PC.