Unless you have very high quality rear/side surround speakers, it's unlikely that high-end interconnects for those channels is going to make any discernable difference in sound quality. Put your best interconnects on the front channels - L, C, and R -- where you will hear the difference. I also agree generally with Distortion's comment that there MAY be a valid reason to use the same brand of interconnect for all channels, but unless there is a vast difference in the quality of the front vs. rear interconnects (e.g., using the most expensive model for the front channels, and the cheapest model for the surrounds), you probably won't hear any difference.