The block thing on the RS Fusion cable is a ferrite 'filter.' It's supposed to filter out Radio Frequency. I've heard of them used on power cords, but have also heard they dull the sound when used on speaker cables or interconnects.
This forum isn't the friendliest place for discussing cables. I've observed a noticeable difference in sound quality between different interconnects and speaker cable, although more expensive does not always mean better.
My personal favorite speaker wire are the Mapleshade Clearview Double Golden Helix Plus and Monster micro flat elect. That's just me, your opinions sure may differ.
There are some terrific values out there for interconnects - my favorite for the dollar are the Tara Labs Prism 300i's, which can be had from a fellow named audiovideoman on ebay for a song - much, much less than the RS Fusion cables.
