Is it best to choose one manufacturer for pc, interconnects and speaker cable (the whole is better than the sum of its parts type of argument) or should each component be tested one at a time and each one be judged on its merit?
This is a common question, which will always provide controversy. Ultimately, you pay your money, so you will have to answer this question for yourself.
I know some folks who have had success running all the same brand of cables/cords. That has never worked for me though, and I have tried a LOT of cables cords.
For me it seems that the more I get of one brand, the more I become aware of the flaws of that particular cable line.
I have had better success balancing the sound to my tastes by mixing and matching.
Good luck.